Monitoring Cancer at the Nano-Level – University of Waterloo


Waterloo QC Cancer 5c7d5fb4c0cfd

Tapered nanowire array device design. Credit: Nature Nanotechnology (2019). DOI: 10.1038/s41565-019-0393-2

How a new quantum sensor could improve cancer treatment

The development of medical imaging and monitoring methods has profoundly impacted the diagnosis and treatment of cancer. These non-invasive techniques allow health care practitioners to look for cancer in the body and determine if treatment is working.

But current techniques have limitations; namely, tumours need to be a specific size to be visible. Being able to detect cancer cells, even before there are enough to form a tumour, is a challenge that researchers around the world are looking to solve.

The solution may lie in nanotechnology

Researchers at the University of Waterloo’s Institute for Quantum Computing (IQC) have developed a quantum sensor that is promising to outperform existing technologies in monitoring the success of cancer treatments.

Sensor image

 Artist’s rendering of the interaction of incident single photon pulses and a tapered semiconductor nanowire array photodetector.

 

“A sensor needs to be very efficient at detecting light,” explains principal investigator Michael Reimer, an IQC faculty member and professor in the Faculty of Engineering. “What’s unique about our sensor is that the light can be absorbed all the way, from UV to infrared. No commercially available device exists that can do that now.”

 

Current sensors reflect some of the light, and depending on the material, this reflection can add up to 30 percent of the light not being absorbed.

This next-generation quantum sensor designed in Reimer’s lab is very efficient and can detect light at the fundamental limit — a single photon — and refresh for the next one within nanoseconds. Researchers created an array of tapered nanowires that turn incoming photons into electric current that can be amplified and detected.

When applied to dose monitoring in cancer treatment, this enhanced ability to detect every photon means that a health practitioner could monitor the dose being given with incredible precision — ensuring enough is administered to kill the cancer cells, but not too much that it also kills healthy cells.

Moving quantum technology beyond the lab

Reimer published his findings in Nature Nanotechnology in March and is now working on a prototype to begin testing outside of his lab. Reimer’s goal is to commercialize the sensor in the next three to five years.

“I enjoy the fundamental research, but I’m also interested in bringing my research out of the lab and into the real world and making an impact to society,” says Reimer.

He is no stranger to bringing quantum technology to the marketplace. While completing his post doctorate at the Delft University of Technology in The Netherlands, Reimer was an integral part of the startup, Single Quantum, developing highly efficient single-photon detectors based on superconducting nanowires.

Reimer’s latest sensor has a wide range of applications beyond dose monitoring for cancer treatments. The technology also has the ability to significantly improve high-speed imaging from space and long-range, high-resolution 3D images.

“A broad range of industries and research fields will benefit from a quantum sensor with these capabilities,” said Reimer. “It impacts quantum communication to quantum lidar to biological applications. Anywhere you have photon-starved situations, you would want an efficient sensor.”

He is exploring all industries and opportunities to put this technology to use.

Breakthroughs come in unexpected places

After earning his undergraduate degree in physics at the University of Waterloo, Reimer moved to Germany to play professional hockey. While taking graduate courses at the Technical University of Munich, he met a professor of nanotechnology who sparked his interest in the field.

“I played hockey and science was my hobby,” says Reimer. “Science is still my hobby, and it’s amazing that it is now my job.” Reimer went on to complete his PhD at the University of Ottawa/National Research Council of Canada, and turned his attention to quantum light sources. Reimer is an internationally renowned expert in quantum light sources and sensors. The idea for the quantum sensor came from his initial research in quantum light sources.

“To get the light out from the quantum light source, we had to come up with a way that you don’t have reflections, so we made this tapered shape. We realized that if we can get the light out that way we could also do the reverse — that’s where the idea for the sensor came from.”

Reimer will be at the Waterloo Innovation Summit on October 1, to present his latest breakthrough and its potential impact on the health care sector. And while he works to bring the sensor to market, Reimer’s lab continues to push the boundaries of quantum photonics.

From discovering the path to perfect photon entanglement to developing novel solid-state quantum devices, Reimer’s research is advancing technologies that could disrupt a multitude of industries and research fields.

Scientists ‘Reverse Time’ with a Quantum Computer


“Now the thing about time is that time isn’t really real.

It’s just your point of view, how does it feel to you?

Einstein said we could never understand it all … “

James Taylor ~ “The Secret of Life”

Researchers from the Moscow Institute of Physics and Technology teamed up with colleagues from the U.S. and Switzerland and returned the state of a quantum computer a fraction of a second into the past.

They also calculated the probability that an electron in empty interstellar space will spontaneously travel back into its recent past. The study is published in Scientific Reports.

“This is one in a series of papers on the possibility of violating the . That law is closely related to the notion of the arrow of time that posits the one-way direction of time from the past to the future,” said the study’s lead author Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information Technology at MIPT.

“We began by describing a so-called local perpetual motion machine of the second kind. Then, in December, we published a paper that discusses the violation of the second law via a device called a Maxwell’s demon,” Lesovik said. “The most recent paper approaches the same problem from a third angle: We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.”

What makes the future different from the past

Most laws of physics make no distinction between the future and the past. For example, let an equation describe the collision and rebound of two identical billiard balls. If a close-up of that event is recorded with a camera and played in reverse, it can still be represented by the same equation. Moreover, it is not possible to distinguish from the recording if it has been doctored. Both versions look plausible. It would appear that the billiard balls defy the intuitive sense of time.

However, imagine recording a cue ball breaking the pyramid, the billiard balls scattering in all directions. In that case, it is easy to distinguish the real-life scenario from reverse playback. What makes the latter look so absurd is our intuitive understanding of the second law of thermodynamics—an isolated system either remains static or evolves toward a state of chaos rather than order.

Most other laws of physics do not prevent rolling billiard balls from assembling into a pyramid, infused tea from flowing back into the tea bag, or a volcano from “erupting” in reverse.

But these phenomena are not observed, because they would require an isolated system to assume a more ordered state without any outside intervention, which runs contrary to the second law. The nature of that law has not been explained in full detail, but researchers have made great headway in understanding the basic principles behind it.

Read More: “Quantum Time Travel”

Spontaneous time reversal

Quantum physicists from MIPT decided to check if time could spontaneously reverse itself at least for an individual particle and for a tiny fraction of a second. That is, instead of colliding billiard balls, they examined a solitary electron in empty interstellar space.

“Suppose the electron is localized when we begin observing it. This means that we’re pretty sure about its position in space. The laws of quantum mechanics prevent us from knowing it with absolute precision, but we can outline a small region where the electron is localized,” says study co-author Andrey Lebedev from MIPT and ETH Zurich.

The physicist explains that the evolution of the electron state is governed by Schrödinger’s equation. Although it makes no distinction between the future and the past, the region of space containing the electron will spread out very quickly. That is, the system tends to become more chaotic. The uncertainty of the electron’s position is growing. This is analogous to the increasing disorder in a large-scale system—such as a billiard table—due to the second law of thermodynamics.

The four stages of the actual experiment on a quantum computer mirror the stages of the thought experiment involving an electron in space and the imaginary analogy with billiard balls. Each of the three systems initially evolves from order toward chaos, but then a perfectly timed external disturbance reverses this process. Credit: @tsarcyanide/MIPT

“However, Schrödinger’s equation is reversible,” adds Valerii Vinokur, a co-author of the paper, from the Argonne National Laboratory, U.S.

“Mathematically, it means that under a certain transformation called complex conjugation, the equation will describe a ‘smeared’ electron localizing back into a small region of space over the same time period.”

Although this phenomenon is not observed in nature, it could theoretically happen due to a random fluctuation in the cosmic microwave background permeating the universe.

The team set out to calculate the probability to observe an electron “smeared out” over a fraction of a second spontaneously localizing into its recent past. It turned out that even across the entire lifetime of the universe—13.7 billion years—observing 10 billion freshly localized electrons every second, the reverse evolution of the particle’s state would only happen once. And even then, the electron would travel no more than a mere one ten-billionth of a second into the past.

Large-scale phenomena involving billiard balls and volcanoes obviously unfold on much greater timescales and feature an astounding number of  and other particles. This explains why we do not observe old people growing younger or an ink blot separating from the paper.

Reversing time on demand

The researchers then attempted to reverse time in a four-stage experiment. Instead of an electron, they observed the state of a quantum computer made of two and later three basic elements called superconducting qubits.

  • Stage 1: Order. Each qubit is initialized in the ground state, denoted as zero. This highly ordered configuration corresponds to an electron localized in a small region, or a rack of billiard balls before the break.
  • Stage 2: Degradation. The order is lost. Just like the electron is smeared out over an increasingly large region of space, or the rack is broken on the pool table, the state of the qubits becomes an ever more complex changing pattern of zeros and ones. This is achieved by briefly launching the evolution program on the quantum computer. Actually, a similar degradation would occur by itself due to interactions with the environment. However, the controlled program of autonomous evolution will enable the last stage of the experiment.
  • Stage 3: Time reversal. A special program modifies the state of the quantum computer in such a way that it would then evolve “backwards,” from chaos toward order. This operation is akin to the random microwave background fluctuation in the case of the electron, but this time, it is deliberately induced. An obviously far-fetched analogy for the billiards example would be someone giving the table a perfectly calculated kick.
  • Stage 4: Regeneration. The evolution program from the second stage is launched again. Provided that the “kick” has been delivered successfully, the program does not result in more chaos but rather rewinds the state of the qubits back into the past, the way a smeared electron would be localized or the billiard balls would retrace their trajectories in reverse playback, eventually forming a triangle.

The researchers found that in 85 percent of the cases, the two-qubit quantum computer returned back into the initial state. When three qubits were involved, more errors happened, resulting in a roughly 50 percent success rate. According to the authors, these errors are due to imperfections in the actual quantum computer. As more sophisticated devices are designed, the error rate is expected to drop.

Interestingly, the time reversal algorithm itself could prove useful for making quantum computers more precise. “Our algorithm could be updated and used to test programs written for computers and eliminate noise and errors,” Lebedev explained.

More information: Scientific Reports(2019). DOI: 10.1038/s41598-019-40765-6

Provided by Moscow Institute of Physics and Technology

Explore further: Quantum Maxwell’s demon ‘teleports’ entropy out of a qubit

The US and China are in a Quantum Arms Race that will Transform Future Warfare


stealth bomber 03f9261bb3c481551b60cbf6fc87adc9

Radar that can spot stealth aircraft and other quantum innovations could give their militaries a strategic edge

In the 1970s, at the height of the Cold War, American military planners began to worry about the threat to US warplanes posed by new, radar-guided missile defenses in the USSR and other nations. In response, engineers at places like US defense giant Lockheed Martin’s famous “Skunk Works” stepped up work on stealth technology that could shield aircraft from the prying eyes of enemy radar.

The innovations that resulted include unusual shapes that deflect radar waves—like the US B-2 bomber’s “flying wing” design (above)—as well as carbon-based materials and novel paints. Stealth technology isn’t yet a Harry Potter–like invisibility cloak: even today’s most advanced warplanes still reflect some radar waves. But these signals are so small and faint they get lost in background noise, allowing the aircraft to pass unnoticed.

China and Russia have since gotten stealth aircraft of their own, but America’s are still better. They have given the US the advantage in launching surprise attacks in campaigns like the war in Iraq that began in 2003.

This advantage is now under threat. In November 2018, China Electronics Technology Group Corporation (CETC), China’s biggest defense electronics company, unveiled a prototype radar that it claims can detect stealth aircraft in flight. The radar uses some of the exotic phenomena of quantum physics to help reveal planes’ locations.

It’s just one of several quantum-inspired technologies that could change the face of warfare. As well as unstealthing aircraft, they could bolster the security of battlefield communications and affect the ability of submarines to navigate the oceans undetected. The pursuit of these technologies is triggering a new arms race between the US and China, which sees the emerging quantum era as a once-in-a-lifetime opportunity to gain the edge over its rival in military tech.

Stealth spotter

How quickly quantum advances will influence military power will depend on the work of researchers like Jonathan Baugh. A professor at the University of Waterloo in Canada, Baugh is working on a device that’s part of a bigger project to develop quantum radar. Its intended users: stations in the Arctic run by the North American Aerospace Defense Command, or NORAD, a joint US-Canadian organization.

Baugh’s machine generates pairs of photons that are “entangled”—a phenomenon that means the particles of light share a single quantum state. A change in one photon immediately influences the state of the other, even if they are separated by vast distances.

Quantum radar operates by taking one photon from every pair generated and firing it out in a microwave beam. The other photon from each pair is held back inside the radar system.

Equipment from a prototype quantum radar system made by China Electronics Technology Group Corporation IMAGINECHINA VIA AP IMAGES

Only a few of the photons sent out will be reflected back if they hit a stealth aircraft. A conventional radar wouldn’t be able to distinguish these returning photons from the mass of other incoming ones created by natural phenomena—or by radar-jamming devices. But a quantum radar can check for evidence that incoming photons are entangled with the ones held back. Any that are must have originated at the radar station. This enables it to detect even the faintest of return signals in a mass of background noise.

Baugh cautions that there are still big engineering challenges. These include developing highly reliable streams of entangled photons and building extremely sensitive detectors. It’s hard to know if CETC, which already claimed in 2016 that its radar could detect objects up to 100 kilometers (62 miles) away, has solved these challenges; it’s keeping the technical details of its prototype a secret.

Seth Lloyd, an MIT professor who developed the theory underpinning quantum radar, says that in the absence of hard evidence, he’s skeptical of the Chinese company’s claims. But, he adds, the potential of quantum radar isn’t in doubt. When a fully functioning device is finally deployed, it will mark the beginning of the end of the stealth era.

China’s ambitions

CETC’s work is part of a long-term effort by China to turn itself into a world leader in quantum technology. The country is providing generous funding for new quantum research centers at universities and building a national research center for quantum science that’s slated to open in 2020. It’s (China) already leaped ahead of the US in registering patents in quantum communications and cryptography.

A study of China’s quantum strategy published in September 2018 by the Center for a New American Security (CNAS), a US think tank, noted that the Chinese People’s Liberation Army (PLA) is recruiting quantum specialists, and that big defense companies like China Shipbuilding Industry Corporation (CSIC) are setting up joint quantum labs at universities. Working out exactly which projects have a military element to them is hard, though. “There’s a degree of opacity and ambiguity here, and some of that may be deliberate,” says Elsa Kania, a coauthor of the CNAS study.

China’s efforts are ramping up just as fears are growing that the US military is losing its competitive edge. A commission tasked by Congress to review the Trump administration’s defense strategy issued a report in November 2018 warning that the US margin of superiority “is profoundly diminished in key areas” and called for more investment in new battlefield technologies.

One of those technologies is likely to be quantum communication networks. Chinese researchers have already built a satellite that can send quantum-encrypted messages between distant locations, as well as a terrestrial network that stretches between Beijing and Shanghai. Both projects were developed by scientific researchers, but the know-how and infrastructure could easily be adapted for military use.

The networks rely on an approach known as quantum key distribution (QKD). Messages are encoded in the form of classical bits, and the cryptographic keys needed to decode them are sent as quantum bits, or qubits. These qubits are typically photons that can travel easily across fiber-optic networks or through the atmosphere. If an enemy tries to intercept and read the qubits, this immediately destroys their delicate quantum state, wiping out the information they carry and leaving a telltale sign of an intrusion.

QKD technology isn’t totally secure yet. Long ground networks require way stations  similar to the repeaters that boost signals along an ordinary data cable. At these stations, the keys are decoded into classical form before being re-encoded in a quantum form and sent to the next station. While the keys are in classical form, an enemy could hack in and copy them undetected.

To overcome this issue, a team of researchers at the US Army Research Laboratory in Adelphi, Maryland, is working on an approach called quantum teleportation. This involves using entanglement to transfer data between a qubit held by a sender and another held by a receiver, using what amounts to a kind of virtual, one-time-only quantum data cable. (There’s a more detailed description here.)

Michael Brodsky, one of the researchers, says he and his colleagues have been working on a number of technical challenges, including finding ways to ensure that the qubits’ delicate quantum state isn’t disrupted during transmission through fiber-optic networks. The technology is still confined to a lab, but the team says it’s now robust enough to be tested outside. “The racks can be put on trucks, and the trucks can be moved to the field,” explains Brodsky. china teleport 2014-10-22_quantum

It may not be long before China is testing its own quantum teleportation system. Researchers are already building the fiber-optic network for one that will stretch from the city of Zhuhai, near Macau, to some islands in Hong Kong.

Quantum compass

Researchers are also exploring using quantum approaches to deliver more accurate and foolproof navigation tools to the military. US aircraft and naval vessels already rely on precise atomic clocks to help keep track of where they are. But they also count on signals from the Global Positioning System (GPS), a network of satellites orbiting Earth. This poses a risk because an enemy could falsify, or “spoof,” GPS signals—or jam them altogether.

Lockheed Martin thinks American sailors could use a quantum compass based on microscopic synthetic diamonds with atomic flaws known as nitrogen-vacancy centers, or NV centers. These quantum defects in the diamond lattice can be harnessed to form an extremely accurate magnetometer. Shining a laser on diamonds with NV centers makes them emit light at an intensity that varies according to the surrounding magnetic field.

Ned Allen, Lockheed’s chief scientist, says the magnetometer is great at detecting magnetic anomalies—distinctive variations in Earth’s magnetic field caused by magnetic deposits or rock formations. There are already detailed maps of these anomalies made by satellite and terrestrial surveys. By comparing anomalies detected using the magnetometer against these maps, navigators can determine where they are. Because the magnetometer also indicates the orientation of magnetic fields, ships and submarines can use them to work out which direction they are heading.

China’s military is clearly worried about threats to its own version of GPS, known as BeiDou. Research into quantum navigation and sensing technology is under way at various institutes across the country, according to the CNAS report.

As well as being used for navigation, magnetometers can also detect and track the movement of large metallic objects, like submarines, by fluctuations they cause in local magnetic fields. Because they are very sensitive, the magnetometers are easily disrupted by background noise, so for now they are used for detection only at very short distances. But last year, the Chinese Academy of Sciences let slip that some Chinese researchers had found a way to compensate for this using quantum technology. That might mean the devices could be used in the future to spot submarines at much longer ranges.

A tight race

It’s still early days for militaries’ use of quantum technologies. There’s no guarantee they will work well at scale, or in conflict situations where absolute reliability is essential. But if they do succeed, quantum encryption and quantum radar could make a particularly big impact. Code-breaking and radar helped change the course of World War II. Quantum communications could make stealing secret messages much harder, or impossible. Quantum radar would render stealth planes as visible as ordinary ones. Both things would be game-changing.

It’s also too early to tell whether it will be China or the US that comes out on top in the quantum arms race—or whether it will lead to a Cold War–style stalemate. But the money China is pouring into quantum research is a sign of how determined it is to take the lead.

China has also managed to cultivate close working relationships between government research institutes, universities, and companies like CSIC and CETC. The US, by comparison, has only just passed legislation to create a national plan for coordinating public and private efforts. The delay in adopting such an approach has led to a lot of siloed projects and could slow the development of useful military applications. “We’re trying to get the research community to take more of a systems approach,” says Brodsky, the US army quantum expert.

qubit-type-and-year

U.S. Leads World in Quantum Computing Patent Filings with IBM Leading the Charge

Still, the US military does have some distinct advantages over the PLA. The Department of Defense has been investing in quantum research for a very long time, as have US spy agencies. The knowledge generated helps explains why US companies lead in areas like the development of powerful quantum computers, which harness entangled qubits to generate immense amounts of processing power.

The American military can also tap into work being done by its allies and by a vibrant academic research community at home. Baugh’s radar research, for instance, is funded by the Canadian government, and the US is planning a joint research initiative with its closest military partners—Canada, the UK, Australia, and New Zealand—in areas like quantum navigation.

All this has given the US has a head start in the quantum arms race. But China’s impressive effort to turbocharge quantum research means the gap between them is closing fast.

MIT: Physicists record ‘lifetime’ of graphene qubits – Foundation for Advancing Quantum Computing


 

Researchers from MIT and elsewhere have recorded, for the first time, the “temporal coherence” of a graphene qubit

The demonstration, which used a new kind of graphene-based qubit, meaning how long it can maintain a special state that allows it to represent two logical states simultaneously, represents a critical step forward for practical quantum computing, the researchers say.

Superconducting quantum bits (simply, qubits) are artificial atoms that use various methods to produce bits of quantum information, the fundamental component of quantum computers. Similar to traditional binary circuits in computers, qubits can maintain one of two states corresponding to the classic binary bits, a 0 or 1.

But these qubits can also be a superposition of both states simultaneously, which could allow quantum computers to solve complex problems that are practically impossible for traditional computers.

The amount of time that these qubits stay in this superposition state is referred to as their “coherence time.” The longer the coherence time, the greater the ability for the qubit to compute complex problems.

Recently, researchers have been incorporating graphene-based materials into superconducting quantum computing devices, which promise faster, more efficient computing, among other perks.

Until now, however, there’s been no recorded coherence for these advanced qubits, so there’s no knowing if they’re feasible for practical quantum computing. In a paper published today in Nature Nanotechnology, the researchers demonstrate, for the first time, a coherent qubit made from graphene and exotic materials.

These materials enable the qubit to change states through voltage, much like transistors in today’s traditional computer chips — and unlike most other types of superconducting qubits. Moreover, the researchers put a number to that coherence, clocking it at 55 nanoseconds, before the qubit returns to its ground state.

The work combined expertise from co-authors William D. Oliver, a physics professor of the practice and Lincoln Laboratory Fellow whose work focuses on quantum computing systems, and Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT who researches innovations in graphene.

“Our motivation is to use the unique properties of graphene to improve the performance of superconducting qubits,” says first author Joel I-Jan Wang, a postdoc in Oliver’s group in the Research Laboratory of Electronics (RLE) at MIT.

“In this work, we show for the first time that a superconducting qubit made from graphene is temporally quantum coherent, a key requisite for building more sophisticated quantum circuits. Ours is the first device to show a measurable coherence time — a primary metric of a qubit — that’s long enough for humans to control.”

There are 14 other co-authors, including Daniel Rodan-Legrain, a graduate student in Jarillo-Herrero’s group who contributed equally to the work with Wang; MIT researchers from RLE, the Department of Physics, the Department of Electrical Engineering and Computer Science, and Lincoln Laboratory; and researchers from the Laboratory of Irradiated Solids at the École Polytechnique and the Advanced Materials Laboratory of the National Institute for Materials Science.

A pristine graphene sandwich

Superconducting qubits rely on a structure known as a “Josephson junction,” where an insulator (usually an oxide) is sandwiched between two superconducting materials (usually aluminum).

In traditional tunable qubit designs, a current loop creates a small magnetic field that causes electrons to hop back and forth between the superconducting materials, causing the qubit to switch states.

But this flowing current consumes a lot of energy and causes other issues. Recently, a few research groups have replaced the insulator with graphene, an atom-thick layer of carbon that’s inexpensive to mass produce and has unique properties that might enable faster, more efficient computation.

To fabricate their qubit, the researchers turned to a class of materials, called van der Waals materials — atomic-thin materials that can be stacked like Legos on top of one another, with little to no resistance or damage.

These materials can be stacked in specific ways to create various electronic systems. Despite their near-flawless surface quality, only a few research groups have ever applied van der Waals materials to quantum circuits, and none have previously been shown to exhibit temporal coherence.

For their Josephson junction, the researchers sandwiched a sheet of graphene in between the two layers of a van der Waals insulator called hexagonal boron nitride (hBN). Importantly, graphene takes on the superconductivity of the superconducting materials it touches.

The selected van der Waals materials can be made to usher electrons around using voltage, instead of the traditional current-based magnetic field. Therefore, so can the graphene — and so can the entire qubit.

 

When voltage gets applied to the qubit, electrons bounce back and forth between two superconducting leads connected by graphene, changing the qubit from ground (0) to excited or superposition state (1). The bottom hBN layer serves as a substrate to host the graphene.

The top hBN layer encapsulates the graphene, protecting it from any contamination. Because the materials are so pristine, the traveling electrons never interact with defects. This represents the ideal “ballistic transport” for qubits, where a majority of electrons move from one superconducting lead to another without scattering with impurities, making a quick, precise change of states.

How voltage helps

The work can help tackle the qubit “scaling problem,” Wang says. Currently, only about 1,000 qubits can fit on a single chip. Having qubits controlled by voltage will be especially important as millions of qubits start being crammed on a single chip.

“Without voltage control, you’ll also need thousands or millions of current loops too, and that takes up a lot of space and leads to energy dissipation,” he says.

Additionally, voltage control means greater efficiency and a more localized, precise targeting of individual qubits on a chip, without “cross talk.” That happens when a little bit of the magnetic field created by the current interferes with a qubit it’s not targeting, causing computation problems.

For now, the researchers’ qubit has a brief lifetime. For reference, conventional superconducting qubits that hold promise for practical application have documented coherence times of a few tens of microseconds, a few hundred times greater than the researchers’ qubit.

But the researchers are already addressing several issues that cause this short lifetime, most of which require structural modifications. They’re also using their new coherence-probing method to further investigate how electrons move ballistically around the qubits, with aims of extending the coherence of qubits in general.

Coherent control of a hybrid superconducting circuit made with graphene-based van der Waals heterostructures
Joel I-Jan Wang, Daniel Rodan-Legrain, Landry Bretheau, Daniel L. Campbell, Bharath Kannan, David Kim, Morten Kjaergaard, Philip Krantz, Gabriel O. Samach, Fei Yan, Jonilyn L. Yoder, Kenji Watanabe, Takashi Taniguchi, Terry P. Orlando, Simon Gustavsson, Pablo Jarillo-Herrero & William D. Oliver
Nature Nanotechnology (2018)
DOI: 10.1038_s41565-018-0329-2

Contact information:

William D. Oliver
MIT Physics Professor of the Practice
oliver@ll.mit.edu URL: http://www.rle.mit.edu/

Pablo Jarillo-Herrero
MIT Physics Professor
pjarillo@mit.edu URL: http://jarilloherrero.mit.edu/

Massachusetts Institute of Technology (MIT)

 

Four Emerging Technology Areas That Will Help Define Our World In 2019


Welcome to 2019....

2018 was surely a transformative year for technological innovation. We saw early development of ambient computing, quantum teleportation, cloaks of invisibility, genomics advancements and even robocops.

Granted we’re not flying around in our own cars like the Jetsons did yet, but we’re closer. In 2019 we will continue on the transformation path and expand even more into adopting cutting edge immersive technologies.

What’s ahead for the coming year? I envision four emerging technology areas that will significantly impact our lives in 2019.

1.  The Internet of Things and Smart Cities

The Internet of Things (IoT) refers to the general idea of devices and equipment that are readable, recognizable, locatable, addressable, and/or controllable via the internet. 

This includes everything from home appliances, wearable technology and cars. These days, if a device can be turned on, it most likely can be connected to the internet. Because of this, data can be shared quickly across a multitude of objects and devices increasing the rate of communications.

Cisco, who terms the “Internet of Things,” “The Internet of Everything,” predicts that 50 billion devices (including our smartphones, appliances and office equipment) will be wirelessly connected via a network of sensors to the internet by 2020.

The term “Smart City” connotes creating a public/private infrastructure to conduct activities that protect and secure citizens. The concept of Smart Cities integrates communications (5-G), transportation, energy, water resources, waste collections, smart-building technologies, and security technologies and services. They are the cities of the future.

IoT is the cog of Smart Cities that integrates these resources, technologies, services and infrastructure.

The research firm Frost & Sullivan estimates the combined global market potential of Smart City segments (transportation, healthcare, building, infrastructure, energy and governance) to be $1.5 Trillion ($20B by 2050 on sensors alone according to Navigant Technology).

The combined growth of IoT and Smart Cities will be a force to reckon with in 2019!

     2.  Artificial Intelligence (AI)

Emergent artificial intelligence (AI), machine learning, human-computer interface, and augmented reality technologies are no longer science fiction. Head-spinning technological advances allow us to gain greater data-driven insights than ever before.

The ethical debate about AI is fervent over the threatening implications of future technologies that can think like a human (or better) and make their own decisions. The creation of a “Hal” type entity as depicted in Stanley Kubrick’s film, 2001 A Space Odyssey, is not far-fetched.

To truly leverage our ability to use data driven insights we need to make sure our thinking about how to best use this data keeps pace with its availability.

The vast majority of digital data is unstructured: a complex mesh of images, texts, videos and other data formats. Estimates suggest 80-90 percent of the world’s data is unstructured and growing at an increasingly rapid rate each day.

To even begin to make sense of this much data, advanced technologies are required. Artificial intelligence is the means by which this data is processed today, and it’s already a part of your everyday life.

In 2019, companies and governments will continue to develop technology that distributes artificial intelligence and machine learning software to millions of graphics and computer processors around the world. The question is how far away are we from a “Hal” with the ability for human analysis and techno emotions? 

     3.  Quantum Computing

The world of computing has witnessed seismic advancements since the invention of the electronic calculator in the 1960s. The past few years in information processing have been especially transformational.

What were once thought of as science fiction fantasies are now technological realities. Classical computing has become more exponentially faster and more capable and our enabling devices smaller and more adaptable.

We are starting to evolve beyond classical computing into a new data era called quantum computing. It is envisioned that quantum computing will accelerate us into the future by impacting the landscape of artificial intelligence and data analytics.

The quantum computing power and speed will help us solve some of the biggest and most complex challenges we face as humans.

Gartner describes quantum computing as: “[T]he use of atomic quantum states to effect computation. Data is held in qubits (quantum bits), which have the ability to hold all possible states simultaneously. Data held in qubits is affected by data held in other qubits, even when physically separated.

This effect is known as entanglement.” In a simplified description, quantum computers use quantum bits or qubits instead of using binary traditional bits of ones and zeros for digital communications.

Futurist Ray Kurzweil said that mankind will be able to “expand the scope of our intelligence a billion-fold” and that “the power of computing doubles, on average, every two years.” Recent breakthroughs in physics, nanotechnology and materials science have brought us into a computing reality that we could not have imagined a decade ago.

As we get closer to a fully operational quantum computer, a new world of supercomputing beckons that will impact on almost every aspect of our lives. In 2019 we are inching closer.

     4.  Cybersecurity (and Risk Management)

Many corporations, organizations and agencies have continued to be breached throughout 2018 despite cybersecurity investments on information assurance. The cyber threats grow more sophisticated and deadly with each passing year. The firm Gemalto estimated that data breaches compromised 4.5 billion records in first half of 2018. And a University of Maryland study found that hackers now attack computers every 39 seconds.

In 2019 we will be facing a new and more sophisticated array of physical security and cybersecurity challenges (including automated hacker tools) that pose significant risk to people, places and commercial networks.

The nefarious global threat actors are terrorists, criminals, hackers, organized crime, malicious individuals, and in some cases, adversarial nation states.

The physical has merged with the digital in the cybersecurity ecosystem. The more digitally interconnected we become in our work and personal lives, the more vulnerable we will become. Now everyone and anything connected is a target.

Cybersecurity is the digital glue that keeps IoT, Smart Cities, and our world of converged machines, sensors, applications and algorithms operational.

Addressing the 2019 cyber-threat also requires incorporating a better and more calculated risk awareness and management security strategy by both the public and private sectors. A 2019 cybersecurity risk management strategy will need to be comprehensive, adaptive and elevated to the C-Suite. 

I have just touched on a few of the implications of four emerging technology areas that will have significant impact in our lives in 2019.

These areas are just the tip of the iceberg as we really are in the midst of a paradigm shift in applied scientific knowledge.  We have entered a new renaissance of accelerated technological development that is exponentially transforming our civilization.

Yet with these benefits come risks. With such catalyzing innovation, we cannot afford to lose control. The real imperative for this new year is for planning and systematic integration.  

Hopefully that will provide us with a guiding technological framework that will keep us prosperous and safe.

Article by Chuck Brooks Special to Forbes Magazine
Chuck Brooks is an Advisor and Contributor to Cognitive World. In his full time role he is the Principal Market Growth Strategist for General Dynamics Mission Systems…MORE

‘Quantum Internet’ – Moving toward ‘Unhackable’ Communications and how Single Particles of Light could make it Possible: Purdue University – Next Step ‘On-Chip Circuitry’


towardunhack
Purdue researchers have created a new light source that generates at least 35 million photons per second, increasing the speed of quantum communication. Credit: Massachusetts Institute of Technology image/Mikhail Shalaginov

Hacker attacks on everything from social media accounts to government files could be largely prevented by the advent of quantum communication, which would use particles of light called “photons” to secure information rather than a crackable code.

The problem is that quantum communication is currently limited by how much   can help send securely, called a “secret bit rate.” Purdue University researchers created a new technique that would increase the secret bit rate 100-fold, to over 35 million photons per second.

“Increasing the bit rate allows us to use single photons for sending not just a sentence a second, but rather a relatively large piece of information with extreme security, like a megabyte-sized file,” said Simeon Bogdanov, a Purdue postdoctoral researcher in electrical and computer engineering.

Eventually, a high  will enable an ultra-secure “quantum internet,” a network of channels called “waveguides” that will transmit single photons between devices, chips, places or parties capable of processing quantum information.

“No matter how computationally advanced a hacker is, it would be basically impossible by the laws of physics to interfere with these quantum communication channels without being detected, since at the quantum level,  and matter are so sensitive to disturbances,” Bogdanov said.

The work was first published online in July for inclusion in a print Nano Letters issue on August 8, 2018.

Using light to send information is a game of probability: Transmitting one bit of information can take multiple attempts. The more photons a light source can generate per second, the faster the rate of successful information transmission.

Toward unhackable communication: Single particles of light could bring the 'quantum internet'
The Purdue University Quantum Center, including Simeon Bogdanov (left) and Sajid Choudhury (right), is investigating how to advance quantum communication for practical uses. Credit: Purdue University image/Susan Fleck

“A source might generate a lot of photons per second, but only a few of them may actually be used to transmit information, which strongly limits the speed of quantum communication,” Bogdanov said.

For faster  , Purdue researchers modified the way in which a light pulse from a laser beam excites electrons in a man-made “defect,” or local disturbance in a crystal lattice, and then how this defect emits one  at a time.

The researchers sped up these processes by creating a new light source that includes a tiny diamond only 10 nanometers big, sandwiched between a silver cube and silver film. Within the nanodiamond, they identified a single defect, resulting from one atom of carbon being replaced by nitrogen and a vacancy left by a missing adjacent carbon atom.

The nitrogen and the missing atom together formed a so-called “nitrogen-vacancy center” in a diamond with electrons orbiting around it.

A metallic antenna coupled to this defect facilitated the interaction of photons with the orbiting electrons of the nitrogen-vacancy center, through hybrid light-matter particles called “plasmons.” By the center absorbing and emitting one plasmon at a time, and the nanoantenna converting the plasmons into photons, the rate of generating photons for  became dramatically faster.

“We have demonstrated the brightest single-photon source at room temperature. Usually sources with comparable brightness only operate at very low temperatures, which is impractical for implementing on computer chips that we would use at room temperature,” said Vlad Shalaev, the Bob and Anne Burnett Distinguished Professor of Electrical and Computer Engineering.

Next, the researchers will be adapting this system for on-chip circuitry. This would mean connecting the plasmonic antenna with waveguides so that photons could be routed to different parts of the chip rather than radiating in all directions.

 Explore further: Physicists demonstrate new method to make single photons

More information: Simeon I. Bogdanov et al. Ultrabright Room-Temperature Sub-Nanosecond Emission from Single Nitrogen-Vacancy Centers Coupled to Nanopatch Antennas, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b01415

Tiny camera lens may help link quantum computers to network


Tiny Camerra Lens 180913142057_1_540x360
Kai Wang holding a sample that has multiple metasurface camera lenses.
Credit: Lannon Harley, ANU

An international team of researchers led by The Australian National University (ANU) has invented a tiny camera lens, which may lead to a device that links quantum computers to an optical fibre network.

Quantum computers promise a new era in ultra-secure networks, artificial intelligence and therapeutic drugs, and will be able to solve certain problems much faster than today’s computers.

The unconventional lens, which is 100 times thinner than a human hair, could enable a fast and reliable transfer of quantum information from the new-age computers to a network, once these technologies are fully realised.

The device is made of a silicon film with millions of nano-structures forming a metasurface, which can control light with functionalities outperforming traditional systems.

Associate Professor Andrey Sukhorukov said the metasurface camera lens was highly transparent, thereby enabling efficient transmission and detection of information encoded in quantum light.

“It is the first of its kind to image several quantum particles of light at once, enabling the observation of their spooky behaviour with ultra-sensitive cameras,” said Associate Professor Sukhorukov, who led the research with a team of scientists at the Nonlinear Physics Centre of the ANU Research School of Physics and Engineering.

Kai Wang, a PhD scholar at the Nonlinear Physics Centre who worked on all aspects of the project, said one challenge was making portable quantum technologies.

“Our device offers a compact, integrated and stable solution for manipulating quantum light. It is fabricated with a similar kind of manufacturing technique used by Intel and NVIDIA for computer chips.” he said.

The research was conducted at the Nonlinear Physics Centre laboratories, where staff and postgraduate scholars developed and trialled the metasurface camera lens in collaboration with researchers at the Oak Ridge National Laboratory in the United States and the National Central University in Taiwan.

Story Source:

Materials provided by Australian National UniversityNote: Content may be edited for style and length.


Journal Reference:

  1. Kai Wang, James G. Titchener, Sergey S. Kruk, Lei Xu, Hung-Pin Chung, Matthew Parry, Ivan I. Kravchenko, Yen-Hung Chen, Alexander S. Solntsev, Yuri S. Kivshar, Dragomir N. Neshev, Andrey A. Sukhorukov. Quantum metasurface for multiphoton interference and state reconstructionScience, 2018; 361 (6407): 1104-1108 DOI: http://dx.doi.org/10.1126/science.aat8196

Novel Nano-Materials for Quantum Electronics and more …


novelnanomatThe use of redox-active organic molecules and magnetic metal ions as molecular building blocks for materials represents a new strategy towards novel types of 2D materials exhibiting both high electronic conductivity and magnetic order. Credit: Kasper Steen Pedersen and We Love People.

An international team led by Assistant Professor Kasper Steen Pedersen, DTU Chemistry, has synthesized a novel nano material with electrical and magnetic properties making it suitable for future quantum computers and other applications in electronics.

Chromium-chloride-pyrazine (chemical formula CrCl2(pyrazine)2) is a layered material, which is a precursor for a so-called 2-D material. In principle, a 2-D material has a thickness of just a single molecule and this often leads to properties very different from those of the same material in a normal 3-D version; not least of which, the electrical properties will differ. While in a 3-D material, electrons are able to take any direction, in a 2-D material they will be restricted to moving horizontally—as long as the wavelength of the electron is longer than the thickness of the 2-D layer.

Organic/inorganic hybrid

Graphene is the most well-known 2-D material. Graphene consists of  in a lattice structure, which yields its remarkable strength. Since the first synthesis of graphene in 2004, hundreds of other 2-D materials have been synthesized, some of which may be candidates for  electronics applications. However, the novel material is based on a very different concept. While the other candidates are all inorganic—just like graphene—chromium-chloride-pyrazine is an organic/inorganic hybrid material.

“The material marks a new type of chemistry, in which we are able to replace various building blocks in the material and thereby modify its physical and chemical properties. This cannot be done in graphene. For example, one can’t choose to replace half the carbon atoms in  with another kind of atom. Our approach allows designing properties much more accurately than known in other 2-D materials,” Kasper Steen Pedersen explains.

Novel nano material for quantum electronics
The use of redox-active organic molecules and magnetic metal ions as molecular building blocks for materials represents a new strategy towards novel types of 2D materials exhibiting both high electronic conductivity and magnetic order. Credit: Kasper Steen Pedersen and We Love People.

Besides the electrical properties, also the magnetic properties in Chromium-Chloride-Pyrazine can be accurately designed. This is especially relevant in relation to “spintronics”.

Watch a Video from Danish Technical Institute on ‘Nanomaterials for Printed Electronics

 

“While in normal electronics, only the charge of the electrons is utilized, But also electron spin—which is a quantum mechanical property—is used in . This is highly interesting for quantum computing applications. Therefore, development of nano-scale materials which are both conducting and magnetic is most relevant,” Kasper Steen Pedersen notes.

A new world of 2-D materials

Besides quantum computing, chromium-chloride-pyrazine may be of interest in future superconductors, catalysts, batteries, fuel cells, and electronics in general.

Companies are not keen to begin producing the material right away, the researcher stresses: “Not yet, at least! This is still fundamental research. Since we are suggesting a material synthesized from an entirely novel approach, a number of questions remain unanswered. For instance, we are not yet able to determine the degree of stability of the material in various applications. However, even if chromium-chloride-pyrazine should for some reason prove unfit for the various possible applications, the new principles behind its synthesis will still be relevant. This is the door to a new world of more advanced 2-D  opening up.”

 Explore further: New chemical method could revolutionize graphene

More information: Kasper S. Pedersen et al, Formation of the layered conductive magnet CrCl2(pyrazine)2 through redox-active coordination chemistry, Nature Chemistry (2018). DOI: 10.1038/s41557-018-0107-7

Read more at: https://phys.org/news/2018-09-nano-material-quantum-electronics.html#jCp

The reality of quantum computing could be … just three years away


Quantum computing has moved out of the realm of theoretical physics and into the real world, but its potential and promise are still years away.

Onstage at TechCrunch Disrupt SF, a powerhouse in the world of quantum research and a young upstart in the field presented visions for the future of the industry that illustrated both how far the industry has come and how far the technology has to go.

For both Dario Gil, the chief operating officer of IBM Research and the company’s vice president of artificial intelligence and quantum computing, and Chad Rigetti, a former IBM researcher who founded Rigetti Computing and serves as its chief executive, the moment that a quantum computer will be able to perform operations better than a classical computer is only three years away.

“[It’s] generating a solution that is better, faster or cheaper than you can do otherwise,” said Rigetti. “Quantum computing has moved out of a field of research into now an engineering discipline and an engineering enterprise.”

Considering the more than 30 years that IBM has been researching the technology and the millions (or billions) that have been poured into developing it, even seeing an end of the road is a victory for researchers and technologists.

Achieving this goal, for all of the brainpower and research hours that have gone into it, is hardly academic.

The Chinese government is building a $10 billion National Laboratory for Quantum Information in Anhui province, which borders Shanghai and is slated to open in 2020. Meanwhile, the U.S. public research into quantum computing is running at around $200 million per year.

Source: Patin Informatics via Bloomberg News.

One of the reasons why governments, especially, are so interested in the technology is its potential to completely remake the cybersecurity landscape. Some technologists argue that quantum computers will have the potential to crack any type of encryption technology, opening up all of the networks in the world to potential hacking.

The quantum computing apocalypse is imminent

According to experts, quantum computers will be able to create breakthroughs in many of the most complicated data processing problems, leading to the development of new medicines, building molecular structures and doing analysis going far beyond the capabilities of today’s binary computers.

Of course, quantum computing is so much more than security. It will enable new ways of doing things we can’t even imagine because we have never had this much pure compute power. Think about artificial and machine learning or drug development; any type of operation that is compute-intensive could benefit from the exponential increase in compute power that quantum computing will bring.

Security may be the Holy Grail for governments, but both Rigetti and Gil say that the industrial chemical business will be the first place where the potentially radical transformation of a market will appear first.

What is quantum computing anyway?

To understand quantum computing it helps to understand the principles of the physics behind it.

As Gil explained onstage (and on our site), quantum computing depends on the principles of superposition, entanglement and interference.

A Turning Point For Quantum Computing

Quantum computing is moving from theory and experimentation into engineering and applications. But now that quantum computing is going mainstream, it is incumbent on businesses and governments to understand its potential, for universities to beef up their teaching programs in quantum computing and related subjects and for students to become aware of promising new career paths.

Superposition is the notion that physicists can observe multiple potential states of a particle. “If you a flip a coin it is one or two states,” said Gil. Meaning that there’s a single outcome that can be observed. But if someone were to spin a coin, they’d see a number of potential outcomes.

Once you’ve got one particle that’s being observed, you can add another and pair them thanks to a phenomenon called quantum entanglement. “If you have two coins where each one can be in superpositions and then you can have measurements can be taken” of the difference of both.

Finally, there’s interference, where the two particles can be manipulated by an outside force to change them and create different outcomes.

“In classical systems you have these bits of zeros and ones and the logical operations of the ands and the ors and the nots,” said Gil. “The classical computer is able to process the logical operations of bits expressed in zeros and ones.”

“In an algorithm you put the computer in a super positional state,” Gil continued. “You can take the amplitude and states and interfere them and the algorithm is the thing that interferes… I can have many, many states representing different pieces of information and then i can interfere with it to get these data.”

These operations are incredibly hard to sustain. In the early days of research into quantum computing the superconducting devices only had one nanosecond before a qubit transforms into a traditional bit of data. Those ranges have increased between 50 and 100 microseconds, which enabled IBM and Rigetti to open up their platforms to researchers and others to conduct experimentation (more on that later).

The physical quantum computer

As one can imagine, dealing with quantum particles is a delicate business. So the computing operations have to be carefully controlled. At the base of the machine is what basically amounts to a huge freezer that maintains a temperature in the device of 15 millikelvin — near absolute zero degrees and 180 times colder than the temperatures in interstellar space.

“These qubits are very delicate,” said Gil. “Anything from the outside world can couple to it and destroy its state and one way to protect it is to cool it.”

Wiring for the quantum computer is made of superconducting coaxial cables. The inputs to the computers are microwave pulses that manipulates the particles creating a signal that is then interpreted by the computers’ operators.

Those operators used to require a degree in quantum physics. But both IBM and Rigetti have been working on developing tools that can enable a relative newbie to use the tech.

Quantum computing in the “cloud”

Even as companies like IBM and Rigetti bring the cost of quantum computing down from tens of millions of dollars to roughly $1 million to $2 million, these tools likely will never become commodity hardware that a consumer buys to use as a personal computer.

Rather, as with most other computing these days, quantum computing power will be provided as a service to users.

Indeed, Rigetti announced onstage a new hybrid computing platform that can provide computing services to help the industry both reach quantum advantage — that tipping point at which quantum is commercially viable — and to enable industries to explore the technologies to acclimatize to the potential ways in which typical operations could be disrupted by it.

Rigetti announces its hybrid quantum computing platform — and a $1M prize

Rigetti, a quantum computing startup that is challenging the likes of IBM, Microsoft and Google in this nascent space, today at our TechCrunch Disrupt SF 2018 event announced the launch of its new hybrid quantum computing platform. While Rigetti already offered API access to its quantum computing platform, this new service, dubbed Quantum Cloud Services … Continue reading

“A user logs on to their own device and use our software development kit to write a quantum application,” said Rigetti. “That program is sent to a compiler and kicks off an optimization kit that runs on a quantum and classical computer… This is the architecture that’s needed to achieve quantum advantage.”

Both IBM and Rigetti — and a slew of other competitors — are preparing users for accessing quantum computing opportunities on the cloud.

IBM has more than a million chips performing millions of quantum operations requested by users in over 100 countries around the world.

“In a cloud-first era I’m not sure the economic forces will be there that will drive us to develop the miniaturized environment in the laptop,” Rigetti said. But the ramifications of the technology’s commercialization will be felt by everyone, everywhere.

“Quantum computing is going to change the world and it’s all going to come in our lifetime, whether that’s two years or five years,” he said. “Quantum computing is going to redefine every industry and touch every market. Every major company will be involved in some capacity in that space.”

MIT: Fish-eye lens may entangle pairs of atoms – may be a promising vehicle for necessary building blocks in designing quantum computers


MIT-Fish-Eye_0

James Maxwell was the first to realize that light is able to travel in perfect circles within the fish-eye lens because the density of the lens changes, with material being thickest at the middle and gradually thinning out toward the edges.

Nearly 150 years ago, the physicist James Maxwell proposed that a circular lens that is thickest at its center, and that gradually thins out at its edges, should exhibit some fascinating optical behavior. Namely, when light is shone through such a lens, it should travel around in perfect circles, creating highly unusual, curved paths of light.

He also noted that such a lens, at least broadly speaking, resembles the eye of a fish. The lens configuration he devised has since been known in physics as Maxwell’s fish-eye lens — a theoretical construct that is only slightly similar to commercially available fish-eye lenses for cameras and telescopes.

Now scientists at MIT and Harvard University have for the first time studied this unique, theoretical lens from a quantum mechanical perspective, to see how individual atoms and photons may behave within the lens. In a study published Wednesday in Physical Review A, they report that the unique configuration of the fish-eye lens enables it to guide single photons through the lens, in such a way as to entangle pairs of atoms, even over relatively long distances.

Entanglement is a quantum phenomenon in which the properties of one particle are linked, or correlated, with those of another particle, even over vast distances. The team’s findings suggest that fish-eye lenses may be a promising vehicle for entangling atoms and other quantum bits, which are the necessary building blocks for designing quantum computers.

“We found that the fish-eye lens has something that no other two-dimensional device has, which is maintaining this entangling ability over large distances, not just for two atoms, but for multiple pairs of distant atoms,” says first author Janos Perczel, a graduate student in MIT’s Department of Physics. “Entanglement and connecting these various quantum bits can be really the name of the game in making a push forward and trying to find applications of quantum mechanics.”

The team also found that the fish-eye lens, contrary to recent claims, does not produce a perfect image. Scientists have thought that Maxwell’s fish-eye may be a candidate for a “perfect lens” — a lens that can go beyond the diffraction limit, meaning that it can focus light to a point that is smaller than the light’s own wavelength. This perfect imaging, scientist predict, should produce an image with essentially unlimited resolution and extreme clarity.

However, by modeling the behavior of photons through a simulated fish-eye lens, at the quantum level, Perczel and his colleagues concluded that it cannot produce a perfect image, as originally predicted.

“This tells you that there are these limits in physics that are really difficult to break,” Perczel says. “Even in this system, which seemed to be a perfect candidate, this limit seems to be obeyed. Perhaps perfect imaging may still be possible with the fish eye in some other, more complicated way, but not as originally proposed.”

Perczel’s co-authors on the paper are Peter Komar and Mikhail Lukin from Harvard University.

A circular path

Maxwell was the first to realize that light is able to travel in perfect circles within the fish-eye lens because the density of the lens changes, with material being thickest at the middle and gradually thinning out toward the edges. The denser a material, the slower light moves through it. This explains the optical effect when a straw is placed in a glass half full of water. Because the water is so much denser than the air above it, light suddenly moves more slowly, bending as it travels through water and creating an image that looks as if the straw is disjointed.

In the theoretical fish-eye lens, the differences in density are much more gradual and are distributed in a circular pattern, in such a way that it curves rather bends light, guiding light in perfect circles within the lens.

In 2009, Ulf Leonhardt, a physicist at the Weizmann Institute of Science in Israel was studying the optical properties of Maxwell’s fish-eye lens and observed that, when photons are released through the lens from a single point source, the light travels in perfect circles through the lens and collects at a single point at the opposite end, with very little loss of light.

“None of the light rays wander off in unwanted directions,” Perczel says. “Everything follows a perfect trajectory, and all the light will meet at the same time at the same spot.”

Leonhardt, in reporting his results, made a brief mention as to whether the fish-eye lens’ single-point focus might be useful in precisely entangling pairs of atoms at opposite ends of the lens.

“Mikhail [Lukin] asked him whether he had worked out the answer, and he said he hadn’t,” Perczel says. “That’s how we started this project and started digging deeper into how well this entangling operation works within the fish-eye lens.”

Playing photon ping-pong

To investigate the quantum potential of the fish-eye lens, the researchers modeled the lens as the simplest possible system, consisting of two atoms, one at either end of a two-dimensional fish-eye lens, and a single photon, aimed at the first atom. Using established equations of quantum mechanics, the team tracked the photon at any given point in time as it traveled through the lens, and calculated the state of both atoms and their energy levels through time.

They found that when a single photon is shone through the lens, it is temporarily absorbed by an atom at one end of the lens. It then circles through the lens, to the second atom at the precise opposite end of the lens. This second atom momentarily absorbs the photon before sending it back through the lens, where the light collects precisely back on the first atom.

“The photon is bounced back and forth, and the atoms are basically playing ping pong,” Perczel says. “Initially only one of the atoms has the photon, and then the other one. But between these two extremes, there’s a point where both of them kind of have it. It’s this mind-blowing quantum mechanics idea of entanglement, where the photon is completely shared equally between the two atoms.”

Perczel says that the photon is able to entangle the atoms because of the unique geometry of the fish-eye lens. The lens’ density is distributed in such a way that it guides light in a perfectly circular pattern and can cause even a single photon to bounce back and forth between two precise points along a circular path.

“If the photon just flew away in all directions, there wouldn’t be any entanglement,” Perczel says. “But the fish-eye gives this total control over the light rays, so you have an entangled system over long distances, which is a precious quantum system that you can use.”

As they increased the size of the fish-eye lens in their model, the atoms remained entangled, even over relatively large distances of tens of microns. They also observed that, even if some light escaped the lens, the atoms were able to share enough of a photon’s energy to remain entangled. Finally, as they placed more pairs of atoms in the lens, opposite to one another, along with corresponding photons, these atoms also became simultaneously entangled.

“You can use the fish eye to entangle multiple pairs of atoms at a time, which is what makes it useful and promising,” Perczel says.

Fishy secrets

In modeling the behavior of photons and atoms in the fish-eye lens, the researchers also found that, as light collected on the opposite end of the lens, it did so within an area that was larger than the wavelength of the photon’s light, meaning that the lens likely cannot produce a perfect image.

“We can precisely ask the question during this photon exchange, what’s the size of the spot to which the photon gets recollected? And we found that it’s comparable to the wavelength of the photon, and not smaller,” Perczel says. “Perfect imaging would imply it would focus on an infinitely sharp spot. However, that is not what our quantum mechanical calculations showed us.”

Going forward, the team hopes to work with experimentalists to test the quantum behaviors they observed in their modeling. In fact, in their paper, the team also briefly proposes a way to design a fish-eye lens for quantum entanglement experiments.

“The fish-eye lens still has its secrets, and remarkable physics buried in it,” Perczel says. “But now it’s making an appearance in quantum technologies where it turns out this lens could be really useful for entangling distant quantum bits, which is the basic building block for building any useful quantum computer or quantum information processing device.”