Daily Archives: August 17, 2020

That could help with the design of quantum computers

Aug 15th 2020

IN RAY BRADBURYs science-fiction story A Sound of Thunder, a character time-travels far into the past and inadvertently crushes a butterfly underfoot. The consequences of that minuscule change ripple through reality such that, upon the time-travellers return, the present has been dramatically changed.

The butterfly effect describes the high sensitivity of many systems to tiny changes in their starting conditions. But while it is a feature of classical physics, it has been unclear whether it also applies to quantum mechanics, which governs the interactions of tiny objects like atoms and fundamental particles. Bin Yan and Nikolai Sinitsyn, a pair of physicists at Los Alamos National Laboratory, decided to find out. As they report in Physical Review Letters, quantum-mechanical systems seem to be more resilient than classical ones. Strangely, they seem to have the capacity to repair damage done in the past as time unfolds.

To perform their experiment, Drs Yan and Sinitsyn ran simulations on a small quantum computer made by IBM. They constructed a simple quantum system consisting of qubitsthe quantum analogue of the familiar one-or-zero bits used by classical computers. Like an ordinary bit, a qubit can be either one or zero. But it can also exist in superposition, a chimerical mix of both states at once.

Having established the system, the authors prepared a particular qubit by setting its state to zero. That qubit was then allowed to interact with the others in a process called quantum scrambling which, in this case, mimics the effect of evolving a quantum system backwards in time. Once this virtual foray into the past was completed, the authors disturbed the chosen qubit, destroying its local information and its correlations with the other qubits. Finally, the authors performed a reversed scrambling process on the now-damaged system. This was analogous to running the quantum system all the way forwards in time to where it all began.

They then checked to see how similar the final state of the chosen qubit was to the zero-state it had been assigned at the beginning of the experiment. The classical butterfly effect suggests that the researchers meddling should have changed it quite drastically. In the event, the qubits original state had been almost entirely recovered. Its state was not quite zero, but it was, in quantum-mechanical terms, 98.3% of the way there, a difference that was deemed insignificant. The final output state after the forward evolution is essentially the same as the input state before backward evolution, says Dr Sinitsyn. It can be viewed as the same input state plus some small background noise. Oddest of all was the fact that the further back in simulated time the damage was done, the greater the rate of recoveryas if the quantum system was repairing itself with time.

The mechanism behind all this is known as entanglement. As quantum objects interact, their states become highly correlatedentangledin a way that serves to diffuse localised information about the state of one quantum object across the system as a whole. Damage to one part of the system does not destroy information in the same way as it would with a classical system. Instead of losing your work when your laptop crashes, having a highly entangled system is a bit like having back-ups stashed in every room of the house. Even though the information held in the disturbed qubit is lost, its links with the other qubits in the system can act to restore it.

The upshot is that the butterfly effect seems not to apply to quantum systems. Besides making life safe for tiny time-travellers, that may have implications for quantum computing, too, a field into which companies and countries are investing billions of dollars. We think of quantum systems, especially in quantum computing, as very fragile, says Natalia Ares, a physicist at the University of Oxford. That this result demonstrates that quantum systems can in fact be unexpectedly robust is an encouraging finding, and bodes well for potential future advances in the field.

This article appeared in the Science & technology section of the print edition under the headline "A flutter in time"

Excerpt from:

Quantum mechanics is immune to the butterfly effect - The Economist

MIP* = RE is not a typo. It is a groundbreaking discovery and the catchy title of a recent paper in the field of quantum complexity theory. Complexity theory is a zoo of complexity classes collections of computational problems of which MIP* and RE are but two.

The 165-page paper shows that these two classes are the same. That may seem like an insignificant detail in an abstract theory without any real-world application. But physicists and mathematicians are flocking to visit the zoo, even though they probably dont understand it all. Because it turns out the discovery has astonishing consequences for their own disciplines.

In 1936, Alan Turing showed that the Halting Problem algorithmically deciding whether a computer program halts or loops forever cannot be solved. Modern computer science was born. Its success made the impression that soon all practical problems would yield to the tremendous power of the computer.

But it soon became apparent that, while some problems can be solved algorithmically, the actual computation will last long after our Sun will have engulfed the computer performing the computation. Figuring out how to solve a problem algorithmically was not enough. It was vital to classify solutions by efficiency. Complexity theory classifies problems according to how hard it is to solve them. The hardness of a problem is measured in terms of how long the computation lasts.

RE stands for problems that can be solved by a computer. It is the zoo. Lets have a look at some subclasses.

The class P consists of problems which a known algorithm can solve quickly (technically, in polynomial time). For instance, multiplying two numbers belongs to P since long multiplication is an efficient algorithm to solve the problem. The problem of finding the prime factors of a number is not known to be in P; the problem can certainly be solved by a computer but no known algorithm can do so efficiently. A related problem, deciding if a given number is a prime, was in similar limbo until 2004 when an efficient algorithm showed that this problem is in P.

Another complexity class is NP. Imagine a maze. Is there a way out of this maze? is a yes/no question. If the answer is yes, then there is a simple way to convince us: simply give us the directions, well follow them, and well find the exit. If the answer is no, however, wed have to traverse the entire maze without ever finding a way out to be convinced.

Such yes/no problems for which, if the answer is yes, we can efficiently demonstrate that, belong to NP. Any solution to a problem serves to convince us of the answer, and so P is contained in NP. Surprisingly, a million dollar question is whether P=NP. Nobody knows.

The classes described so far represent problems faced by a normal computer. But computers are fundamentally changing quantum computers are being developed. But if a new type of computer comes along and claims to solve one of our problems, how can we trust it is correct?

Imagine an interaction between two entities, an interrogator and a prover. In a police interrogation, the prover may be a suspect attempting to prove their innocence. The interrogator must decide whether the prover is sufficiently convincing. There is an imbalance; knowledge-wise the interrogator is in an inferior position.

In complexity theory, the interrogator is the person, with limited computational power, trying to solve the problem. The prover is the new computer, which is assumed to have immense computational power. An interactive proof system is a protocol that the interrogator can use in order to determine, at least with high probability, whether the prover should be believed. By analogy, these are crimes that the police may not be able to solve, but at least innocents can convince the police of their innocence. This is the class IP.

If multiple provers can be interrogated, and the provers are not allowed to coordinate their answers (as is typically the case when the police interrogates multiple suspects), then we get to the class MIP. Such interrogations, via cross examining the provers responses, provide the interrogator with greater power, so MIP contains IP.

Quantum communication is a new form of communication carried out with qubits. Entanglement a quantum feature in which qubits are spookishly entangled, even if separated makes quantum communication fundamentally different to ordinary communication. Allowing the provers of MIP to share an entangled qubit leads to the class MIP*.

It seems obvious that communication between the provers can only serve to help the provers coordinate lies rather than assist the interrogator in discovering truth. For that reason, nobody expected that allowing more communication would make computational problems more reliable and solvable. Surprisingly, we now know that MIP* = RE. This means that quantum communication behaves wildly differently to normal communication.

In the 1970s, Alain Connes formulated what became known as the Connes Embedding Problem. Grossly simplified, this asked whether infinite matrices can be approximated by finite matrices. This new paper has now proved this isnt possible an important finding for pure mathematicians.

In 1993, meanwhile, Boris Tsirelson pinpointed a problem in physics now known as Tsirelsons Problem. This was about two different mathematical formalisms of a single situation in quantum mechanics to date an incredibly successful theory that explains the subatomic world. Being two different descriptions of the same phenomenon it was to be expected that the two formalisms were mathematically equivalent.

But the new paper now shows that they arent. Exactly how they can both still yield the same results and both describe the same physical reality is unknown, but it is why physicists are also suddenly taking an interest.

Time will tell what other unanswered scientific questions will yield to the study of complexity. Undoubtedly, MIP* = RE is a great leap forward.

The rest is here:

Major quantum computational breakthrough is shaking up physics and maths - The Conversation UK

The quantum world is a pretty wild one, where the seemingly impossible happens all the time: Teensy objects separated by miles are tied to one another, and particles can even be in two places at once. But one of the most perplexing quantum superpowers is the movement of particles through seemingly impenetrable barriers.

Now, a team of physicists has devised a simple way to measure the duration of this bizarre phenomenon, called quantum tunneling. And they figured out how long the tunneling takes from start to finish from the moment a particle enters the barrier, tunnels through and comes out the other side, they reported online July 22 in the journal Nature.

Quantum tunneling is a phenomenon where an atom or a subatomic particle can appear on the opposite side of a barrier that should be impossible for the particle to penetrate. It's as if you were walking and encountered a 10-foot-tall (3 meters) wall extending as far as the eye can see. Without a ladder or Spider-man climbing skills, the wall would make it impossible for you to continue.

Related: The 18 biggest unsolved mysteries in physics

However, in the quantum world, it is rare, but possible, for an atom or electron to simply "appear" on the other side, as if a tunnel had been dug through the wall. "Quantum tunneling is one of the most puzzling of quantum phenomena," said study co-author Aephraim Steinberg, co-director of the Quantum Information Science Program at Canadian Institute for Advanced Research. "And it is fantastic that we're now able to actually study it in this way."

Quantum tunneling is not new to physicists. It forms the basis of many modern technologies such as electronic chips, called tunnel diodes, which allow for the movement of electricity through a circuit in one direction but not the other. Scanning tunneling microscopes (STM) also use tunneling to literally show individual atoms on the surface of a solid. Shortly after the first STM was invented, researchers at IBM reported using the device to spell out the letters IBM using 35 xenon atoms on a nickel substrate.

While the laws of quantum mechanics allow for quantum tunneling, researchers still don't know exactly what happens while a subatomic particle is undergoing the tunneling process. Indeed, some researchers thought that the particle appears instantaneously on the other side of the barrier as if it instantaneously teleported there, Sci-News.com reported.

Researchers had previously tried to measure the amount of time it takes for tunneling to occur, with varying results. One of the difficulties in earlier versions of this type of experiment is identifying the moment tunneling starts and stops. To simplify the methodology, the researchers used magnets to create a new kind of "clock" that would tick only while the particle was tunneling.

Subatomic particles all have magnetic properties and when magnets are in an external magnetic field, they rotate like a spinning top. The amount of rotation (also called precession) depends on how long the particle is bathed in that magnetic field. Knowing that, the Toronto group used a magnetic field to form their barrier. When particles are inside the barrier, they precess. Outside it, they don't. So measuring how long the particles precess told the researchers how long those atoms took to tunnel through the barrier.

Related: 18 times quantum particles blew our minds

"The experiment is a breathtaking technical achievement," said Drew Alton, physics professor at Augustana University, in South Dakota.

The researchers prepared approximately 8,000 rubidium atoms, cooled them to a billionth of a degree above absolute zero. The atoms needed to be this temperature, otherwise they would have moved around randomly at high speeds, rather than staying in a small clump. The scientists used a laser to create the magnetic barrier; they focused the laser so that the barrier was 1.3 micrometers (microns) thick, or the thickness of about 2,500 rubidium atoms. (So if you were a foot thick, front to back, this barrier would be the equivalent of about half a mile thick.) Using another laser, the scientists nudged the rubidium atoms toward the barrier, moving them about 0.15 inches per second (4 millimeters/s).

As expected, most of the rubidium atoms bounced off the barrier. However, due to quantum tunneling, about 3% of the atoms penetrated the barrier and appeared on the other side. Based on the precession of those atoms, it took them about 0.6 milliseconds to traverse the barrier.

Chad Orzel, an associate professor of physics at Union College in New York, who was not part of the study, applauded the experiment, "Their experiment is ingeniously constructed to make it difficult to interpret as anything other than what they say," said Orzel, author of "How to Teach Quantum Mechanics to Your Dog" (Scribner, 2010) It "is one of the best examples you'll see of a thought experiment made real," he added.

Experiments exploring quantum tunneling are difficult and further research is needed to understand the implications of this study. The Toronto group is already considering improvements to their apparatus to not only determine the duration of the tunneling process, but to also see if they can learn anything about velocity of the atoms at different points inside the barrier. "We're working on a new measurement where we make the barrier thicker and then determine the amount of precession at different depths," Steinberg said. "It will be very interesting to see if the atoms' speed is constant or not."

In many interpretations of quantum mechanics, it is impossible even in principle to determine a subatomic particle's trajectory. Such a measurement could lead to insights into the confusing world of quantum theory. The quantum world is very different from the world we're familiar with. Experiments like these will help make it a little less mysterious.

Originally published on Live Science.

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Physicists watch quantum particles tunnel through solid barriers. Here's what they found. - Space.com

There arent many aspiring astrophysicists who go on to become strategists, but Publicis Media head of strategy Shann Biglione is the exception. Here, he shares a thought-provoking piece about science, marketing and the contradictions that rule us all.

When I was young and naive, my ambition was to become an astrophysicist. I was starstruck by the cosmos, inebriated by Hubbles imagery and the mind-blowing concepts of Einsteins general relativity. A painstakingly obtained undergraduate in physics later, I realized I wasnt nearly smart enough for rocket science and fittingly decided for a career in marketing instead.

As the years went by and the hairline receded, I found that great marketing is fairly simple, but hard. Yet, we keep celebrating people who want us to believe they make the complicated easy, waving change as a scare tactic or asking us to simply start with the why. And so, we come with perfectly held models that explain it all, billing expensive hours to introduce new paradigms we can pitch in the elevator.

But the more you learn about marketing, the more you realize that being able to entertain seemingly contradicting models is not a bug, but a feature. And after years of trying to make sense of my daily work, there are a few parallels between scientific theory and marketing theory I find titillating to draw. Especially if those literally keep physicists up at night.

As our understanding of quantum scale objects grew, a baffling realization challenged the very definition of how matter operates. Electrons, photons and protons not only carry their properties like particles that move as points in space, but also as waves that ripple through it. Light (photons), when sent through a thin hole, doesnt just send a straight line of its particle through the holes, it projects wave-like patterns that echo behind it. Einstein described this as having two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do.

The together they do part is a very interesting provocation for marketers, one brilliantly entertained a few years ago by Bob AdContrarian Hoffman. In it, Bob drew the parallel with consumer behavior. He argues that we tend to define consumer behavior through either a rational, persuasive lens where they do not throw their money away on stupid crap, or an irrational model where consumers are deeply influenced by emotions and heuristics, often unaware of their true motivations.

The reality is that we have seen evidence for both, and its easy to think one is more important than the other. But like photons, they are more likely explained by their contradictions. One can both display extremely rational behaviors at times all the while being emotionally driven a second later. And yes, there is absolutely value in understanding how to fit either pattern, but its important to remember they are not either/or questions as much as they are an either/and combination.

A second interesting theory is Heisenbergs uncertainty principle (yes, that Heisenberg, although no, not that Heisenberg). It states that the more precisely the position of some particle is determined, the less precisely its momentum can be predicted from initial conditions. We cannot know both accurately at the same time.

It may remind you of the observer principle, which dictates that the mere observation of a phenomenon inevitably changes that phenomenon (for example, running a focus group creates a severe bias in the response). But the uncertainty principle is quite specific about the fact we can define position or momentum, we simply cannot know both at once.

Of course, this is a metaphorical analysis, but I cannot help thinking data (and the way we use it in advertising) often suffers from the same level of uncertainty. We can know that someone has had a connection with a theme, for example through search behaviors or contextual analysis, but we cannot really know why theyre there, or where they are going with this. Could it be, for example, that I am tagged as a sports enthusiast because I was researching the latest Netflix docuseries?

This is not a trivial question to answer for data system, because relying too heavily on data creates dangerous levels of misattribution between provenance, intent and context of the user. And so, it begs the question: would we be more effective as marketers if we made the assumption data-driven marketing is dictated by an uncertainty principle that dispels the illusion of it being deterministic?

One of the most fascinating questions of modern physics is one that Einstein obsessed about until his death: we have completely different theories to explain how the universe works at a macro level than we do for a micro level.

Our understanding of the atomically small is defined by the probabilistic models of quantum field theory, while the world at a cosmic level is currently explained by Einsteins deterministic models of general relativity. Individually, they have worked absolute wonders for human progress: one brought us the magic of modern electronics, the other gives us the GPS and the concept of black holes. But together? Physicists still arent sure how to reconcile the two. There just is a scale at which the laws of one go out of the window while the rules of the other take over.

This was unacceptable to Einstein, and his rejection of a probabilistic model led to one of his most famous quotes: God does not play dice. Decades later, scientists are still trying to solve one of the greatest challenges of modern physics: uncovering a unified theory that makes sense of the small and the big.

Turn to marketing, and the equivalence can be framed in two different ways. Its tempting first to think of the direct parallel with small and big brands. And sure, because their means are very limited small brands tend to operate differently from big brands. But generally, this is more a function of context and operational reality than a true difference in laws of growth.

This is why Byron Sharp, who certainly came closest to a unified theory of marketing, likes to remind us niche just means small when people argue the Ehrenberg-Bass Institutes laws of growth only work for big consumer packages goods companies.

No, where I see a more interesting parallel is with Binet and Fields contrast between short-term and long-term thinking. According to them, marketing works with two different models: one that is emotionally led and mass streamed, another that is more persuasive, and activation based, with more precision in targeting. This has been an increasingly popular theory in the industry, further validated and popularized as part of Mark Ritsons recent analysis of the Effies.

The problem is that this model is often introduced to marketers in an effort to move the pendulum away from something; more recently its been particularly relevant among those where performance marketing obsessed with efficiencies became the new gospel. And like Einstein, people want to believe in a unified theory that speaks to their own bias and dogmas (consumers dont play with dice). Performance marketers remain convinced its still about tracking return on advertising spend on every behavior, just at a bigger scale, while brand marketers think the job is still all about culture.

This misses the core of the message. Its not about being long-term or short-term, its about accepting that both play a role and that every brand needs to strike a balance between the two. Like in physics where the scale you wish to study defines the rules, the ways of marketing can be different depending on the objective youre trying to balance. And thus, hyper targeting may not be the paradigm that defines everything, but remains extremely relevant to an entire side of your plan. Data will provide you lots of actionable behavioral insights, but it wont give you the wider cultural texture. Building the brand will reduce price sensitivity but giving consumers a good understanding of what theyre buying in the first place remains essential.

Marketing in general is a high stakes game decided by a committee of people who are not marketing experts, and so it remains tempting to provide the simplistic view. This is probably why some of the most popular gurus do so well: not because they inspire marketers, but precisely because the simplicity of their recommendation sits well beyond just marketers. Nevertheless, its valuable to find relief in the beauty of balance, nuance, complementarity and yes, just as in physics, sometimes even contradictions.

Shann Biglione is head of strategy, Publicis Media

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The science of marketing: taking inspiration from quantum physics - The Drum

The power of quantum computers creates an unprecedented threat to the security of our data through its potential to break the cryptography that underpins our digital ecosystem. The technology community can address and manage this risk that has the potential to act as a strategic blocker to the wider adoption of Quantum technology; doing so will help unlock the trillion-dollar potential value of quantum technology to the global economy.

For all the dramatic advances they will offer, quantum computers could threaten our ability to encrypt information and exchange it securely. While this development has the potential for significant economic and geopolitical disruption, the technology to mitigate this risk exists today and it also presents a transformative opportunity to deliver a new level of digital trust and security.

What the world needs is a quantum security coalition, a global community of those who are committed to promoting the safe and secure adoption of new quantum applications, promoting better quantum literacy among global leaders, and accelerating a secure global ecosystem, including quantum security technology, that will be able to unlock the true value and potential of this technology securely.

Quantum science is now being harnessed to build a strong cybersecurity response to both a future as well as the current threat landscape. The resultant technologies can provide the basis for a new security foundation that will offer a step-change in our ability to secure our digital infrastructure but we need action now to incentivize their widespread adoption across the digital ecosystem.

Leveraging the laws of physics, quantum-enabled technologies, such as quantum key distribution and quantum random number generation, are not susceptible to attacks from either quantum computers or powerful mathematical techniques. As such they can provide robust and future-proof security and potentially a new paradigm of trust not currently available using traditional approaches.

These physics-based approaches, based on advanced cybersecurity software and next-generation cryptographic strategies (known as post-quantum algorithms), deliver resilient cybersecurity infrastructure capable of safeguarding our digital lives and connected societies today and into the future. Quantum-enabled technologies form the core of the quantum principles that can be employed to assure the security of digital communications. The following examples of potential applications will play a critical role in building trust in the digital ecosystem.:

1. Quantum key distribution technology uses quantum effects to protect the most critical and vulnerable link in the security chain: the exchange of encryption keys between parties. The diagram below illustrates a quantum key distribution system using an optical fibre-based channel to exchange key material, protected by the laws of quantum physics. Adaptations to other channels such as 'over-the-air' quantum key distribution are also maturing.

Quantum key distribution (QKD)

Image: Quintessence Labs

2. Quantum effects can also be harnessed to deliver high-speed streams of truly random (known as full entropy) bits, which can be used to construct high-quality encryption keys. By virtue of being truly random, and thus unpredictable, such keys are more secure. Devices capturing these quantum effects are now mature and are today being deployed in existing technology and infrastructure.

The importance of entropy in security is well illustrated by cautionary tales of what has happened when too much reliance has been placed on deterministic or algorithmic approaches to generating random numbers.

In 2017, Russian hackers cheated casinos out of millions of dollars by targeting weak (software-based) pseudo-random number generation algorithms in slot machines. They used smartphones to record the patterns of the spins of slot machine wheels and then reverse-engineered the underlying random number-generation algorithm. This enabled the hackers to predict the spins and monetize this predictability. As a consequence, the gaming industry has been one of the first to start realizing the potential power of quantum-enabled true random number generation.

The foundations of this new security paradigm are firmly in place; however more work is needed to drive broad adoption. This is a new technology, and within the security ecosystem progress is being made within the academic, innovation labs and specialist technical communities. But within the security field we see two main barriers that the wider community needs to address:

Barrier 1: Maturity and standards

While quantum entropy is a known, highly capable technology for generating encryption keys that is also ready for broad implementation, there still remain barriers to the deployment of other components of the quantum principles, specifically post-quantum algorithms and quantum key distribution. This includes determining which of the proposed post-quantum algorithms will provide the most robust and durable security while minimizing operational impacts and costs. Similarly, there are multiple different types of quantum key distribution under development that meet a range of needs, and potentially causing confusion among early adopters.

Barrier 2: Building the quantum security ecosystem

Currently, there is a major gap in both awareness of and information about the potential applications, risks and security solutions associated with quantum technology. For leaders charged with ensuring the security and integrity of the systems on which businesses rely, there is still hyperbole in the quantum security debate. The community can change this by building quantum literacy at the board and CEO level. This will require actions at the individual as well as the collective leadership level from gaining an inventory of information assets (including shared infrastructure) and developing a comprehensive understanding of risks potentially impacted by quantum technology to building a roadmap identifying key milestones and trigger events.

In parallel, this technology transition requires the urgent development of a pipeline of professionals to implement these principles effectively. The quantum security market alone is expected to grow to globally to $25 billion in just a few short years. The community needs to start investing in skills and the supply ecosystem must start preparing for a quantum-enabled safe and digitally secure posture. The acceleration of government-led initiatives such as those announced in the US, EU, India, Japan, and Australia will also help.

It is imperative that the cybersecurity community begins to build and accelerate its adoption of quantum security technology, and to move its value from the technical to the transformative space. This emerging technology is already being implemented to build a strong cybersecurity response to the potential cryptographic threat, but these new quantum-enabled technologies provide the basis for a new security foundation that will offer a step-change in our ability to secure digital infrastructure.

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Here's why we need to build a quantum security coalition - World Economic Forum