Illustration by Peter Crowther

Christopher Monroe spends his life poking at atoms with light. He arranges them into rings and chains and then massages them with lasers to explore their properties and make basic quantum computers. Last year, he decided to try something seemingly impossible: to create a time crystal.

The name sounds like a prop from Doctor Who, but it has roots in actual physics. Time crystals are hypothetical structures that pulse without requiring any energy — like a ticking clock that never needs winding. The pattern repeats in time in much the same way that the atoms of a crystal repeat in space. The idea was so challenging that when Nobel prizewinning physicist Frank Wilczek proposed the provocative concept1 in 2012, other researchers quickly proved there was no way to create time crystals.

But there was a loophole — and researchers in a separate branch of physics found a way to exploit the gap. Monroe, a physicist at the University of Maryland in College Park, and his team used chains of atoms they had constructed for other purposes to make a version of a time crystal2 (see 'How to create a time crystal'). “I would say it sort of fell in our laps,” says Monroe.

And a group led by researchers at Harvard University in Cambridge, Massachusetts, independently fashioned time crystals out of 'dirty' diamonds3. Both versions, which are published this week in Nature, are considered time crystals, but not how Wilczek originally imagined. “It's less weird than the first idea, but it's still fricking weird,” says Norman Yao, a physicist at the University of California, Berkeley, and an author on both papers.

They are also the first examples of a remarkable type of matter — a collection of quantum particles that constantly changes, and never reaches a steady state. These systems draw stability from random interactions that would normally disrupt other kinds of matter. “This is a new kind of order, one that was previously thought impossible. That's extremely exciting,” says Vedika Khemani, part of the Harvard team and previously part of the group that originally theorized the existence of the new kind of state. Experimental physicists are already plotting how to exploit the traits of these strange systems in quantum computers and super-sensitive magnetic sensors.

Nik Spencer/Nature

Break time

Wilczek dreamt up time crystals as a way to break the rules. The laws of physics are symmetrical in that they apply equally to all points in space and time. Yet many systems violate that symmetry. In a magnet, atomic spins line up rather than pointing in all directions. In a mineral crystal, atoms occupy set positions in space, and the crystal does not look the same if it is shifted slightly. When a transformation causes properties to change, physicists call that symmetry-breaking, and it is everywhere in nature — at the root of magnetism, superconductivity and even the Higgs mechanism that gives all particles mass.

In 2012, Wilczek, now at Stockholm University, wondered why symmetry never broke spontaneously in time and whether it would be possible to create something in which it did. He called it a time crystal. Experimentalists imagined a quantum version of this entity as perhaps a ring of atoms that would rotate endlessly, cycling and returning to its initial configuration. Its properties would be endlessly synchronized in time, just as atom positions are correlated in a crystal. The system would be in its lowest energy state, but its movement would require no external force. It would, in essence, be a perpetual-motion machine, although not one that produces usable energy.

“From a first glance at the idea, one would say this has to be wrong,” says Yao. Almost by definition, a system in its lowest energy state does not vary in time. If it did, that would mean it had excess energy to lose, says Yao, and the rotation would soon halt. “But Frank convinced the community that the problem was more subtle than maybe it seemed to be,” he says. Perpetual motion was not without precedent in the quantum world: in theory, superconductors conduct electricity forever (although the flow is uniform, so they show no variation in time).

“This is a new kind of order, one that was previously thought impossible.”

These conflicting issues swam around the head of Haruki Watanabe as he stepped out of the first oral exam for his PhD at Berkeley. He had been presenting work on symmetry breaking in space, and his supervisor asked him about the wider implications of Wilczek's time crystal. “I couldn't answer the question in that exam, but it interested me,” says Watanabe, who doubted such an entity was even feasible. “I wondered, 'how can I convince people that it's not possible?'”

Together with physicist Masaki Oshikawa at the University of Tokyo, Watanabe began trying to prove his intuitive answer in a mathematically rigorous way. By phrasing the problem in terms of correlations in space and time between distant parts of the system, the pair derived a theorem in 2015 showing that time crystals were impossible to create for any system in its lowest-energy state4. The researchers also verified that time crystals were impossible for any system in equilibrium — one that has reached a steady state of any energy.

To the physics community, the case was clear cut. “That seemed to be a no-go,” says Monroe. But the proof left a loophole. It did not rule out time crystals in systems that have not yet settled into a steady state and are out of equilibrium. Around the world, theorists began thinking about ways to create alternative versions of time crystals.

Particle soup

When the breakthrough came, it arrived from an unlikely corner of physics, where researchers weren't thinking about time crystals at all.

Shivaji Sondhi, a theoretical physicist at Princeton University, New Jersey, and his colleagues were looking at what happened when certain isolated quantum systems, made of soups of interacting particles, are repeatedly given a kick. Textbook physics says that the systems should heat up and descend into chaos. But in 2015, Sondhi's team predicted that under certain conditions, they would instead club together to form a phase of matter that doesn't exist in equilibrium — a system of particles that would show subtle correlations never seen before — and that would repeat a pattern in time5.

That proposal caught the attention of Chetan Nayak, one of Wilczek's former students, now at the University of California, Santa Barbara, and at Microsoft's nearby Station Q. Nayak and his colleagues soon realized that this strange form of out-of-equilibrium matter would also be a type of time crystal6. But not Wilczek's kind: it would not be in its lowest energy state, and it would require a regular kick to pulse. But it would gain a steady rhythm that doesn't match that of the instigating kick, and that means it would break time symmetry.

“It's like playing with a jump rope, and somehow our arm goes around twice but the rope only goes around once,” says Yao. This is a weaker kind of symmetry breaking than Wilczek imagined: in his, the rope would oscillate all by itself.

When Monroe heard about this proposed system, he initially didn't understand it. “The more I read about it, the more intrigued I became,” he says.

Georg Kucsko

Last year, he set about trying to form his atoms into a time crystal. The recipe was incredibly complex, but just three ingredients were essential: a force repeatedly disturbing the particles, a way to make the atoms interact with each other and an element of random disorder. The combination of these, Monroe says, ensures that particles are limited in how much energy they can absorb, allowing them to maintain a steady, ordered state.

In his experiment, this meant repeatedly firing alternating lasers at a chain of ten ytterbium ions: the first laser flips their spins and the second makes the spins interact with each other in random ways. That combination caused the atomic spins to oscillate, but at twice the period they were being flipped. More than that, the researchers found that even if they started to flip the system in an imperfect way, such as by slightly changing the frequency of the kicks, the oscillation remained the same. “The system still locked at a very stable frequency,” says Monroe. Spatial crystals are similarly resistant to any attempt to nudge their atoms from their set spacing, he says. “This time crystal has the same thing.”

At Harvard, physicist Mikhail Lukin tried to do something similar, but in a very different system — a 3D chunk of diamond. The mineral was riddled with around 1 million defects, each harbouring a spin. And the diamond's impurities provided a natural disorder. When Lukin and his team used microwave pulses to flip the spins, they saw the system respond at a fraction of the frequency with which it was being disturbed.

“This is an intriguing development, but to some extent it's an abuse of the term”

Physicists agree that the two systems spontaneously break a kind of time symmetry and therefore mathematically fulfil the time-crystal criteria. But there is some debate about whether to call them time crystals. “This is an intriguing development, but to some extent it's an abuse of the term,” says Oshikawa.

Yao says that the new systems are time crystals, but that the definition needs to be narrowed to avoid including phenomena that are already well understood and not nearly so interesting for quantum physicists.

But Monroe and Lukin's creations are exciting for different reasons, too, says Yao. They seem to be the first, and perhaps simplest, examples of a host of new phases that exist in relatively unexplored out-of-equilibrium states, he says. They could also have several practical applications. One could be quantum simulation systems that work at high temperatures. Physicists often use entangled quantum particles at nanokelvin temperatures, close to absolute zero, to simulate complex behaviours of materials that cannot be modelled on a classical computer. Time crystals represent a stable quantum system that exists way above these temperatures — in the case of Lukin's diamond, at room temperature — potentially opening the door to quantum simulations without cryogenics.

Time crystals could also find use in super-precise sensors, says Lukin. His lab already uses diamond defects to detect tiny changes in temperature and magnetic fields. But the approach has limits,because if too many defects are packed in a small space, their interactions destroy their fragile quantum states. In a time crystal, however, the interactions serve to stabilize, rather than disrupt, so Lukin could harness millions of defects together to produce a strong signal — one that is able to efficiently probe living cells and atom-thick materials.

The same principle of stability from interactions could apply more widely in quantum computing, says Yao. Quantum computers show huge promise, but have long struggled with the opposing challenges of protecting the fragile quantum bits that perform calculations, yet keeping them accessible for encoding and reading out information. “You can ask yourself in the future whether one could find phases where interactions stabilize these quantum bits,” says Yao.

The story of time crystals is a beautiful example of how progress often happens when different strands of thought come together, says Roderich Moessner, director of the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany. And it may be, he says, that this particular recipe proves to be just one of many ways to cook up a time crystal. </s> Scientists have recently succeeded in creating a mysterious state of matter known as a time crystal. This exotic state of matter seems to suspend the laws of thermodynamics indefinitely.

Editor's Note: This article was updated on March 9 at 11:20 a.m. E.T.

A bizarre new state of matter known as a time crystal seems to suspend the laws of thermodynamics almost indefinitely, two new experiments suggest.

The time crystal is essentially a collection of atoms or ions that are far apart but still interacting with each other. This form of matter keeps "ticking" indefinitely at a certain frequency, without heating up or creating entropy, the natural state of disorder that always increases in the universe. Time crystals work because of quantum effects, or the bizarre rules describing the menagerie of tiny subatomic particles.

The newly created matter joins a host of other exotic states of matter, such as superconductors, quantum-spin liquids and superfluids.

"We have found a new phase of matter," said study co-author Soonwon Choi, a theoretical physics graduate student at Harvard University. "It's something moving in time while still stable." [The 18 Biggest Unsolved Mysteries in Physics]

While the newfound state of matter is fascinating in itself, it could also pave the way for quantum computers that don't lose information, Choi said.

Time crystal

Physicist Frank Wilczek first proposed the idea of a time crystal in the journal Physical Review Letters in 2012. In that study, he suggested a form of matter that spontaneously breaks "time invariance," a fundamental symmetry in time. The concept of time invariance dictatesthat doing something now would produce the same result as doing the same thing, for example, 1 minute in the future (all other conditions being equal).

In Wilczek's conception, however, the quantum interactions among particles, such as ions or subatomic particles, could create a state of matter that oscillates repeatedly in time, just as a crystal has a structure that repeats in space. That means that if the matter oscillated with a period of 2 minutes, doing something with that matter now would produce different results than doing the same thing 1 minute from now. [Photos: Exotic Time Crystals Created in the Lab]

To understand what this means, imagine two people holding a jump rope and swinging it for a third person doing the jumping. In ordinary states of matter, if the rope makes a circle every second, the person must jump every second. But in a time crystal, it is as if the jumper lifts his or her feet every other time the rope hits the ground, and yet somehow keeps time and does not get entangled in the rope, said study co-author Norman Yao, a physicist at the University of California, Berkeley, who earlier this year developed a theoretical framework for testing time crystals.

More recently, follow-up work that built on Wilczek's idea showed that time crystals could not exist in thermal equilibrium. (A fundamental principle of thermodynamics is that two objects in contact will eventually wind up at the same temperature at the steady state, or thermal equilibrium, of the system.) But soon after, researchers showed that time crystals could exist in dynamic states, when systems are changing quickly and haven't yet reached thermal equilibrium.

Earlier this year, Yao, with Andrew Potter, a physicist at the University of Texas at Austin, and colleagues, developed a theoretical paper that identified key signatures of a time crystal. That paper predicted what would happen when a such a crystal melts into a more humdrum state of matter, and laid out an experimental way to prove the existence of time crystals. Independently, Choi and colleagues developed their own idea for a method of demonstrating the existence of time crystals, and then set out to create such a crystal in the lab.

Suspending thermodynamics

In a pair of studies published today (March 8) in the journal Nature, the researchers showed that time crystals can exist in very different systems.

Here, the setup for creating a time crystal using a diamond filled with nitrogen vacancy defects. These defects act like tiny spins that can be manipulated with laser light to create a time crystal. (Image credit: Georg Kucsko)

Choi and his colleagues based at Harvard University used a diamond filled with 1 million nitrogen vacancy color centers; these are spots in the diamond's carbon crystal lattice where nitrogen atoms have replaced the carbon atoms. Because nitrogen is smaller than carbon, this replacement leaves an empty space in the lattice, and the nitrogen and the empty space can act together as if they are tiny particles with spins. (The vacancies are called color centers because the nitrogen atoms produce color in the diamonds ; in this instance, the diamonds are so full of these defects that they appear black.)

Using lasers and microwave radiation, the team then periodically pulsed these nitrogen vacancies, which then oscillated with a frequency that was half of the frequency of the radiation aimed at them (called the driving frequency).

In a second experiment based at the University of Maryland, Potter, Yao and colleagues trapped 14 ions of ytterbium using laser beams and then manipulated the ions' spins using tightly focused laser beams. Again, the material acted like a time crystal, oscillating at half the driving frequency. For the duration of the experiment, the material did not heat up, despite a lot of energy being pumped into the system, said Potter. That's a sign that the laws of thermodynamics didn't come into play during the duration of the experiment, he added.

For instance, the Harvard group used a system that may not be a perfect time crystal, Potter said. The system didn't heat up much, but it did slowly generate heat.

"They're looking a this charmed existence that will slowly die if they let it run long enough," Potter told Live Science.

By contrast, the University of Maryland experiment could conceivably persist indefinitely, though it used a much smaller number of atoms that stretches the definition of what constitutes a state of matter, Potter said.

But the new findings show that the time crystal does not need to be perfectly isolated from heat and entropy to exhibit its repeating-in-time properties, Yao said. This means it may be surprisingly easy to generate these exotic states of matter, he said.

The truly fascinating thing about these experiments is that they have the potential to suspend the laws of physics indefinitely, Potter said. Like a cup of hot coffee that never reaches room temperature, "extra energy just stays in place and the system never equilibrates to one temperature," Potter said.

However, it's important to note that these time crystals don't "break" the fundamental laws of thermodynamics per se; they just put them off as long as the experiment is running, Potter said.

"Thermodynamics is only ever supposed to describe the long-term behavior once you reach this thermal steady state, so it never describes short-term dynamics before you reach thermal equilibrium," Potter said.

By keeping the system in a dynamic state, then, the new experiments simply hold the matter in a regime in which thermodynamics ordinarily wouldn't apply, he added.

Editor's Note: This article was updated to note that follow-up work showing time crystals could not exist in thermal equilibrium was based on Frank Wilczek's idea, not that of Norman Yao.

Originally published on Live Science. </s> Move over, TARDIS: Scientists just reported that they were able to turn back time by using a quantum computer.

A team of scientists from the Moscow Institute of Physics and Technology, the U.S., and Switzerland, published their findings in Scientific Reports, and said they reversed time by a fraction of a second on an IBM quantum computer, New York Daily News reported. In the report, the scientists also determined the “probability that an electron in empty interstellar space will randomly travel back into its recent past,” Phys.org noted.

According to the report, finding the origin of the “arrow of time” is still a major scientific challenge. The scientists’ experiment challenged the second law of thermodynamics, which dictates the direction of events from the past to the future and involves the transition of energy within a system from usable to unusable, The Daily Mail reported.

Most laws of physics do not make a distinction between the past and future, but the scientists claim that their experiment, which involved “reversing time,” showed that these laws can be violated. For their research, scientists were curious if individual particles could impulsively reverse themselves.

To put this concept to the test, the scientists formulated two separate hypothesis: Time reversal would require supersystem manipulation to occur and “in most cases,” would not likely take place in nature. Second, if a supersystem were to “emerge for some specific situation,” a time reversal would need time that “exceeds the universal lifetime” to work.

The scientists tried to accomplish time reversal for a scattered electron with the help of an IBM quantum computer. For the experiment, the scientists used an “evolution program” that would impact “qubits,” also known as quantum bits. A quantum bit is the “fundamental unit of information in a quantum computer, capable of existing in two states, 0 and 1, at the same time or at a different time,” according to Dictionary.com.

Here’s how it works: Following the launch of the evolution program, the particles would move into a changing pattern of zeros and ones. Following this scattering, a program would alter the computer’s state, enabling it to go backwards to its original state. Next, the evolution pattern would be kickstarted from the second state again and rewind the qubits to their original state and the past.

According to the team, in 85 percent of cases, the two-qubit quantum computer returned back into its original state. When three qubits were involved in testing, more errors occurred, and resulted in an approximately 50 percent success rate. The scientists said the error rate is anticipated to drop as more devices are designed. With this experiment, time reversal can help make quantum computers more accurate in the future. </s> The breakthrough came as they were able to go a fraction of a second into the past. It was discovered by researchers from the Moscow Institute of Physics and Technology (MIPT) who teamed up with experts from the US and Switzerland. They discovered the time travel as they checked if time could spontaneously reverse itself for an individual particle and for a tiny fraction of a second.

The research was also able to calculate the probability that an electron in empty interstellar space will spontaneously travel back into its recent past according to the research published in the journal Scientific Reports. Lead author Gordey Lesovik, head of the Laboratory of the Physics of Quantum Information Technology at MIPT, said: "This is one in a series of papers on the possibility of violating the second law of thermodynamics. “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. "We began by describing a so-called local perpetual motion machine of the second kind. READ MORE: Time travel PROOF? ‘Time traveller’ from 2030 warns Mexico SURRENDERS border to USA

“Then, in December, we published a paper that discusses the violation of the second law via a device called a Maxwell's demon. "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." Study co-author Andrey Lebedev from MIPT and ETH Zurich said: "Suppose the electron is localised 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 localised.”The discovery contradicts the laws of physics, which suggests that time is linear and can only travel in one direction - forward. However, the quantum computer can be described as a semi-time machine and has defied the second law of thermodynamics, which is the arrow of time. By using the computer, researchers were able to unscramble a set of electrons which was akin to pool balls on a table going back in to a starting triangle-formation. </s> An international team of scientists led by researchers at the Moscow Institute of Physics and Technology demonstrated the possibility of time reversal in a development that contradicts the basic laws of physics, Newsweek reported on Wednesday. The researchers were assisted by colleagues in Switzerland and the United States.

Lead researcher Dr Gordey Lesovik, who heads the Laboratory of the Physics of Quantum Information at the Moscow Institute of Physics and Technology, said, “We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time.”

In a study published in the journal Scientific Reports on March 13, the scientists experimentally showcased time reversal by sending a qubit from a more complex state to a simpler one using an algorithm on an IBM quantum computer. A qubit, or quantum bit, is the basic unit of quantum information. It is the quantum version of a computer binary bit, which can be a one or a zero.

The quantum physicists decided to check if time could spontaneously reverse itself, at least for an individual particle, and for a tiny fraction of a second. As a result, they examined a single electron in empty interstellar space.

“Suppose the electron is localised when we begin observing it. This means that we are pretty sure about its position in space,” said the study’s co-author Andrey Lebedev from the Moscow Institute of Physics and Technology. “The laws of quantum mechanics prevent us from knowing it with absolute precision, but we can outline a small region where the electron is localised.”

The researchers attempted to calculate the probability of observing an electron over a fraction of a second spontaneously localising into its recent past. Later, they made the same attempt to reverse time using qubits. They employed a programme to convert the qubits into a more complex pattern of ones and zeros, and then used another programme to bring them back to their original state. This successfully caused the qubits to evolve backwards, from chaos towards order.

The team found that in 85% of the cases, the two-qubit quantum computer returned back to the initial state. However, more errors occurred when a third qubit was introduced, with the success rate falling to around 50%.

“Such an unfortunate growth of the complexity explains why do we not observe such time-reversed objects in nature,” said Lebedev. “The probability of a spontaneous appearance of a time-reversed object [particle of a system of particles] is negligible.” </s> Credit: @tsarcyanide/MIPT

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 second law of thermodynamics. 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.

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 electrons 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 quantum computers and eliminate noise and errors," Lebedev explained.

More information: G. B. Lesovik et al. Arrow of time and its reversal on the IBM quantum computer, Scientific Reports (2019). Journal information: Scientific Reports G. B. Lesovik et al. Arrow of time and its reversal on the IBM quantum computer,(2019). DOI: 10.1038/s41598-019-40765-6 </s> An international team of scientists claims to have reversed time with the help of a quantum computer.

By using electrons and quantum mechanics researchers claim they were able to turn back time in an experiment likened to causing a broken rack of pool balls to roll back into place.

The experiment used quantum computer programs to ‘rewind’ scattered quantum bits or qubits back to their starting points.

Researchers from the Moscow Institute of Physics and Technology, helped by colleagues in Switzerland and the U.S., expect the technique to become more efficient.

“Our findings break ground for investigations of the time reversal and the backward time flow in real quantum systems,” the scientists wrote in their conclusion to ‘Arrow of time and its reversal on IBM Quantum Computer.’

“Another fundamental question is whether it is possible at all to design a quantum algorithm that would perform time-reversal more efficiently.”

The scientists found that, working with just two qubits, time reversal was achieved with a success rate of 85 per cent.

When three qubits were involved more errors occurred and the experiment was successful just half the time. </s> We all mark days with clocks and calendars, but perhaps no timepiece is more immediate than a mirror. The changes we notice over the years vividly illustrate science's "arrow of time" -- the likely progression from order to disorder. We cannot reverse this arrow any more than we can erase all our wrinkles or restore a shattered teacup to its original form.

Or can we?

An international team of scientists led by the U.S. Department of Energy's (DOE) Argonne National Laboratory explored this question in a first-of-its-kind experiment, managing to return a computer briefly to the past. The results, published March 13 in the journal Scientific Reports, suggest new paths for exploring the backward flow of time in quantum systems. They also open new possibilities for quantum computer program testing and error correction.

To achieve the time reversal, the research team developed an algorithm for IBM's public quantum computer that simulates the scattering of a particle. In classical physics, this might appear as a billiard ball struck by a cue, traveling in a line. But in the quantum world, one scattered particle takes on a fractured quality, spreading in multiple directions. To reverse its quantum evolution is like reversing the rings created when a stone is thrown into a pond.

In nature, restoring this particle back to its original state -- in essence, putting the broken teacup back together -- is impossible.

The main problem is that you would need a "supersystem," or external force, to manipulate the particle's quantum waves at every point. But, the researchers note, the timeline required for this supersystem to spontaneously appear and properly manipulate the quantum waves would extend longer than that of the universe itself.

Undeterred, the team set out to determine how this complexity might be overcome, at least in principle. Their algorithm simulated an electron scattering by a two-level quantum system, "impersonated" by a quantum computer qubit -- the basic unit of quantum information -- and its related evolution in time. The electron goes from a localized, or "seen," state, to a scattered one. Then the algorithm throws the process in reverse, and the particle returns to its initial state -- in other words, it moves back in time, if only by a tiny fraction of a second.

Given that quantum mechanics is governed by probability rather than certainty, the odds for achieving this time-travel feat were pretty good: The algorithm delivered the same result 85 percent of the time in a two-qubit quantum computer.

"We did what was considered impossible before," said Argonne senior scientist Valerii Vinokur, who led the research.

The result deepens our understanding of how the second law of thermodynamics -- that a system will always move from order to entropy and not the other way around -- acts in the quantum world. The researchers demonstrated in previous work that, by teleportating information, a local violation of the second law was possible in a quantum system separated into remote parts that could balance each other out.

"The results also give a nod to the idea that irreversibility results from measurement, highlighting the role that the concept of "measurement" plays in the very foundation of quantum physics," said article coauthor Gordey Lesovik of the Moscow Institute of Physics and Technology.

This is the same notion Austrian physicist Erwin Schrödinger captured with his famous thought experiment, in which a cat sealed in a box might remain both dead and alive until its status is monitored somehow. The researchers suspended their particle in this superposition, or form of quantum limbo, by limiting their measurements.

"This was the essential part of our algorithm," Vinokur said. "We measured the state of the system in the very beginning and at the very end, but did not interfere in the middle."

The finding may eventually enable better methods of error correction on quantum computers, where accumulated glitches generate heat and beget new ones. A quantum computer able to effectively jump back and clean up errors as it works could operate far more efficiently.

"At this moment, it's very hard to imagine all the implications this can have," Vinokur said. "I am optimistic, and I believe that it will be many."

The study also begs the question, can the researchers now figure out a way to make older folks young again? "Maybe," Vinokur jokes, "with the proper funding."

The work was done by international team including researchers from the Moscow Institute of Physics and Technology (Gordey Lesovik, Andrey Lebedev, Mikhail Suslov), ETH Zurich (Andrey Lebedev) and Argonne National Laboratory, U.S. (Valerii Vinokur, Ivan Sadovskyy).

Funding for this research was provided by the DOE Office of Science and Strategic Partnership Projects (Swiss National Foundation and the Foundation for the Advancement of Theoretical Physics "BASIS").

Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science.

The U.S. Department of Energy's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit the Office of Science website. </s> March 13 (UPI) -- Physicists in Russia have turned back time using a quantum computer.

For some time, researchers at the Moscow Institute of Physics and Technology have been working to prove the second law of thermodynamics can be violated.

"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," lead researcher Gordey Lesovik said in a news release.

Lesovik and his colleagues have already published two papers on the subject. For the latest study, scientists teamed with physicists in the United States and Switzerland to construct a quantum computer capable of violating the second law.

"We have artificially created a state that evolves in a direction opposite to that of the thermodynamic arrow of time," Lesovik said.

The second law of thermodynamics posits that an isolated system can only remain static or evolve toward a state of chaos. If a video of a cue ball colliding with a pyramid of billiard balls was played backward and forward, the viewer would quickly be able to discern which direction revealed the actual sequence of events. The viewer intuitively understands the second law of thermodynamics.

There are no physical laws that explicitly prevent the violation of the second law, but violations have remained unobserved.

To better understand the odds of the second law being violated, quantum physicists analyzed the behavior individual particles.

"Suppose the electron is localized when we begin observing it," said Andrey Lebedev, who works at both MIPT and ETH Zurich. "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."

Schrödinger's equation describes the evolution of a particle's electron state. The region of space containing the electron quickly expands. Chaos increases as systems scale.

"However, Schrödinger's equation is reversible," said Valerii Vinokur, a researcher at the Argonne National Laboratory in the United States. "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."

Researchers crunched the numbers and found that if 10 billion freshly localized electrons were observed every second for the entirety of the universe's lifetime, 13.7 billion years, only one particle would be observed reversing time -- spontaneously localizing against the arrow of time.

Next, scientists attempted to manufacture a violation of the second law of thermodynamics. They built a quantum computer with two and three superconducting qubits. Physicists used the quantum computer to conduct a four-stage experiment.

Stage one features an ordered state, with each qubit grounded at zero, like a single electron confined to a small localized region. During the second stage, order is lost. Scientists used an evolution program on the quantum computer to trigger the degradation of order, causing the qubits to begin assuming an increasingly complex pattern of zeros and ones, like an electron getting smeared out across a larger and larger region of space.

For stage three, scientists used another program to reverse time, causing the qubits to evolve from chaos to order -- to reground themselves at zero. For stage four, the evolution program is relaunched from the second stage, causing the qubits to reverse time and revert to their earlier state.

When scientists used a two-qubit computer to conduct the four stage experiment, they observed qubits moving from chaos to order every time. When they introduced a third qubit, the computer produced more errors, and the qubits were able to reverse time only half of the time.

Researchers suggest their findings -- published this week in the journal Scientific Reports -- could be used to improve the precision of quantum devices.

"Our algorithm could be updated and used to test programs written for quantum computers and eliminate noise and errors," Lebedev said.
Physicists synthesize space-time crystals for the first time.