Mar 19, 2021
Image: Quantum computer - MIT technology review/mit.edu
Some very clever physicists are performing an experiment on an advanced quantum computer according to scribol.com. What they’re trying to do would appear to go against all the laws of physics, laws that even non-scientists instinctively understand. And if their experiment succeeds, they will have achieved something utterly astonishing within the virtual world in which they’re working.
Before we get into exactly what the researchers were up to, it’s probably a good idea to give some explanation of just what quantum computing is. A regular computer, such as the one on which you’re probably viewing this article right now, uses binary numbers – whether it’s a laptop, desktop, tablet or smartphone. That’s basically a series of zeros and ones which instruct the machine how to operate.
But a quantum computer uses a system that is much more flexible and powerful than mere binary numbers. At its heart are qubits: weird data units that have the capability of being zero and one simultaneously. A machine running on qubits theoretically has the capacity to make massive calculations at lightning speeds, far outstripping a conventional computer in its performance.
You can’t go down to your local tech shop and buy a quantum computer, at least not yet. But even when, or if, you ever can, they’re unlikely to replace regular computers. That’s because everyday computers are likely to be the cheapest and most straightforward way to accomplish conventional computing tasks in the foreseeable future.
However, the enormous computational capacity that quantum computers will be able to unleash will have a number of practical applications which could ultimately be of great benefit. Their power may well allow significant breakthroughs in a variety of fields such as pharmaceuticals, materials science and battery technology.
And the big tech companies are anxious to get a share of the future quantum computing action. I.B.M., Google and Microsoft are some of the household names working flat out to make quantum computing a more accessible reality. Many scientists, on the other hand, see quantum computers as a way to explore the strange world of quantum physics.
To understand quantum computers, the first thing you have to get your head around is the qubits we’ve already mentioned which are at the heart of the machines. A qubit is a subatomic particle, usually either a photon or an electron. Creating and then controlling these particles is the challenge that scientists face in trying to build quantum computers.
Developers have come up with various ways to try and generate qubits. One method is to catch single atoms in electromagnetic fields. These fields are set on a silicon chip which is placed in an ultra-high-vacuum vessel. An alternative approach is to utilize superconducting circuits which have been cooled to extremely low temperatures: colder even than levels found in deep space.
Whatever the method used, the aim is to segregate individual qubits in a way that allows them to be controlled. And control is the key. It turns out that qubits have some extraordinary properties, notably one called entanglement and another dubbed superposition. Let’s start by taking a look at just what superposition means.
As mentioned earlier, the extraordinary thing that qubits can do is represent one and zero simultaneously, and they can do this in a huge number of permutations. Physicists call the property of being capable of existing in different states at the same time superposition. Scientists force qubits into a state of superposition by controlling them with microwave beams or lasers.
And if you combine several qubits together, their calculating power is potentially huge. But in another weird quantum twist, once the qubits have completed their calculations, they degenerate back to a static state of one or zero. But if that sounds puzzling, the concept of entanglement is positively dumbfounding.
As with superposition, entanglement is another property that lends qubits their extraordinary powers. Scientists can create a network of two or more qubits which then operate in one quantum interaction. If the condition of one qubit in the set is altered, the others will instantaneously react to that, regardless of the distance between the two particles.
Even the experts, it seems, are at something of a loss as to how to explain the phenomenon of entanglement. Albert Einstein himself struggled to come up with a convincing explanation of entanglement. In one of his most memorable phrases, quoted recently in The Economist magazine as well in many other places, the great man described entanglement as “spooky action at a distance.”
Mysterious though it may be, entanglement is an essential element of the ability of qubits in quantum computers to vastly outperform conventional machines. If you multiply the number of bits in an everyday computer by two, you double its processing power. But if you add just one extra qubit to a quantum machine, that brings an increase in power that is manyfold.
So if you create a quantum computer with a series of qubits at its heart and combine that with custom-designed algorithms, then you have a machine capable of extraordinary calculating capacity. And that’s what gets scientists and physicists excited. However, it’s not all plain sailing in this new world of quantum computers. There is a major drawback.
In practice, quantum computers have an important flaw. They are much more prone to errors than are conventional machines. This is because of a phenomenon known as decoherence. When qubits operate, they have a tendency to deteriorate and actually disappear. This is because, by its nature, the quantum condition in which they exist is acutely frail.
Quantum physicists talk about “noise,” and it’s this that disrupts qubits, making them prone to decoherence and error. In this context “noise” can be anything from disturbance via temperature variations to uncontrolled vibrations; the phenomenon can cause a qubit to fall out of superposition before it has completed a set of calculations. Departing from superposition means qubits cannot perform their assigned tasks.
To counter this decoherence tendency, researchers put a lot of effort into creating conditions that are as neutral as possible in which the qubits can operate. As we’ve already seen, these efforts to have complete control of the quantum environment include creating vacuums and conducting operations in chambers with extremely low temperatures.
But despite the strenuous efforts of researchers to minimize the “noise” that disturbs the integrity of qubits, all too often they are still affected in ways that cause errors. One answer to the problem is to apply what are called smart quantum algorithms. Another possible solution is to add more qubits to the quantum computer.
Theoretically, the addition of thousands of extra qubits to a quantum computer could iron out inaccuracies in calculations. This machine, with multiple qubits working together to form what is called a single logical qubit, should have a high level of accuracy. However, this configuration would also put a brake on the capabilities of the computer.
And there’s another problem with the thousands-of-combined-qubits model. To date, the highest number of qubits generated by scientists is a puny 128. That’s a long way from the thousands it would take to create a logical qubit. Pundits believe that this means a fully functioning quantum computer may still be years away in the future.
Nevertheless, many physicists are still working away in the hope of achieving what’s known as “quantum supremacy”, the Holy Grail of quantum computing. This rather-woolly-sounding statement of ambition is actually a tightly defined term. When the day comes that a quantum computer can make a calculation beyond the capabilities of even the most powerful of conventional machines, quantum supremacy will have been achieved.
What’s more, it seems that quantum supremacy is a moving target. That’s because computer scientists keep coming up with new algorithms that make conventional computers more powerful. And engineers keep building more efficient supercomputers of the classical kind. But that has not deterred researchers in their hunt for the ultimate quantum computer.
Indeed, some impatient scientists are not prepared to wait until quantum computers have reached their full potential, whenever that might be. There are those who are already working with quantum machines designed by some of the major computer-makers such as the Canadian company D-Wave, the Chinese giant Alibaba and the U.S. firm Rigetti Computing.
And one intriguing development is the creation of virtual quantum machines which exist only in a computing data cloud environment. Indeed, one team of researchers has gone ahead and used a virtual quantum machine to conduct an extraordinary experiment. Their aim was nothing short of reversing the passage of real time.
That’s right; they wanted to use an I.B.M. virtual quantum computer to make time go backwards. In their paper, Arrow of time and its reversal on I.B.M. quantum computer published in February 2018 on the Cornell University website Arxiv.org, they described how they had taken a single virtual quantum particle and reversed its passage through time.
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In an email exchange with The New York Timesnewspaper in May 2019 one of the researchers, Valerii M. Vinokur of Argonne National Laboratory in Lemont, Illinois explained the problem that his team had addressed. Vinokur explained, “We demonstrate that time-reversing even ONE quantum particle is an insurmountable task for nature alone.”
Vinokur continued, “The system comprising two particles is even more irreversible, let alone the eggs – comprising billions of particles – we break to prepare an omelet.” In other words, reversing the process of time was no simple puzzle to which the researchers had turned their attention; rather, it was something akin to trying to unscramble eggs. And although Einstein famously characterized time as being simply another dimension, in one important respect, it is unlike the three others with which we are equally familiar.
Time is different because it only apparently works in one direction. On paper the math that underlies the physical laws that define time can be run forwards or backwards. But in real life time only flows in one direction. It always goes forward – we cannot undo what is already done. Or so it appears.
But the research team, led by the Moscow Institute of Physics and Technology’s Gordey B. Lesovik, wanted to show that the flow of time could be interrupted and even diverted. However, this project did contradict one of the main laws of quantum theory. That law states that a subatomic particle cannot move backwards in time.
But there’s even more complexity to the problem in the shape of what’s called the uncertainty principle. This states that it’s possible to calculate the speed of a subatomic particle, and it’s also possible to work out its position. But the two properties cannot be known at the same time. The best that can be achieved is to define a subatomic particle by a mathematical creation called a wave function.
This wave function offers a measurement which gives the probability of the location of a particle such as an electron. The math that formulates this wave function is called the Schrödinger equation after its creator, the Austrian physicist Erwin Schrödinger. In theory at least, this equation can run either forwards or backwards.
So what our team wanted to do was to try to make Schrödinger’s equation run backwards by using a virtual quantum computer acting upon a virtual subatomic particle. Dr. Vinokur told The New York Times that this exercise was similar to making a moving pool ball return to its original spot. That sounds simple enough.
But in the quantum world there’s a fiendish complication; the uncertainty principle we heard about earlier. As Vinokur pointed out, “Because of the uncertainty principle, the quantum ball will never return back to the point of the origin.” Plus of course, the researchers were not dealing with a solid billiard ball but with a virtual particle defined by a wave function.
So what the researchers were setting out to do was incredibly complex. They wanted to reverse the action of a wave, something that is so complicated that it could not happen in the natural world. And it was a stern challenge. The team described just how monumental this task truly was in their paper. They wrote, “It remains to be seen, whether the irreversibility of time is a fundamental law of nature or whether, on the contrary, it might be circumvented.”
To attempt this, the scientists used a relatively simple quantum computer equipped with only five qubits. And then they further limited the quantum machine’s capacity by employing only two or three of the five available qubits. The researchers progressed their experiment on the possibility of reversing the flow of time by going through four steps.
Lesovik’s team first created a virtual atom. Then they put the two (or three) qubits into a state of entanglement so that change in one would affect the other or others. Next the qubits were forced into a more complex state with microwave radio pulses. Now, this process of increasing complexity was halted. And finally, again using microwave pulses, the researchers treated the qubits with a final burst of energy in an attempt to return them to their previous state.
And the result? In effect, the scientists succeeded in their virtual experiment in reversing time by returning the virtual qubits atom back to an earlier state. But not by much. In fact the reversal of time was measured at one millionth of a second. Nevertheless the team felt that they had indeed achieved their goal of making time change to a backwards direction.
But there those who are skeptical of the authenticity of the experiment conducted by Lesovik and his colleagues. Writing in M.I.T. Technology Review Konstantin Kakaes, an editor of the magazine, discussed the time-reversal paper. He wrote, “The authors claimed to have performed an experiment that opens up lines of research, in their words, toward ‘investigating time reversal and the backward time flow.’”
And Kakaes went on to declare, “If you had difficulty understanding how scientists accomplished such a counterintuitive feat, don’t worry. They didn’t.” So not everyone is entirely convinced by the claim that quantum computing can reverse time. But what we can be sure of is that this new technology computing is highly likely to come up with some unpredictable and astonishing feats in the future.
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