Quantum physics, which deals with very small particles, starting with a single atom, contradicts everything we think about the world around us. Nothing behaves the way it is supposed to, and concepts such as time, space, and causality lose their absolute quality. Nevertheless, even though the very small particles behave differently, they are what make up the universe, which does behave according to the rules of time and space that we know. How can that be? One of the bizarre and unexplained phenomena is called "quantitative entanglement": a particle located in a specific place affects a particle that is very far away from it, with no possibility of a physical transfer of information between them. This effect, however, only takes place if the two particles previously met.
As of now, no one understands how quantum entanglement takes place, but that is no reason not to use it. Only recently, Bar Ilan University inaugurated its QUEST – Quantum Entanglement in Science and Technology - Center, which combines theoretical research and applications of quantum entanglement, and it already has cooperative ventures with the defense and high-tech industries in quantum encryption, quantum measurement, and quantum computing. Seven leading researchers founded the center: Professors Lev Khaykovich, Avi Pe’er, Michael Rosenbluh, Michael Stern, Baruch Barzel, Richard Berkovits, and Emanuele Dalla Torre. Extraordinarily, they are jointly managing the center, without one manager at the top. We met with three of them in an attempt to understand something about quantum entanglement and what they are doing with it.
"Even Albert Einstein didn't understand this," says Rosenbluh. "In classical physics, there are several fundamental principles that everyone accepts now: information cannot move faster than light, the past cannot be changed by an action in the future, and the conservation principle – if we divide a particle with a neutral charge, we get two particles, the sum of whose charges must be zero. Rotational energy is also conserved, meaning that when particles are divided, if one have rotates in one direction, the other half rotates in the other direction, with the same force. In quantum physics, however, at the level of a single atom or lower, something goes wrong with these precepts. It's the third, less intuitive, principle of conservation of mass, charge, and rotational energy that remains valid, as if at the expense of the first two fundamentals. Let's assume that we have split a photon - a particle of light. The two halves are complementary in charge, polarization, and mass. In other words, if we knew the original particle that we split and measured one of the split particles, we'll immediately know the state of the second split particle. The strange thing is that as soon as we change one of the split particles, the other half of the particle changes in the same way. This happens only if they are both quanta, i.e. subatomic.
"This concept of quantum entanglement is not simple and not so logical. Even Einstein was unwilling to accept it, and went on saying that he didn't understand it. At the end of his life, however, he was persuaded that it was true, and today, after many years of work, we have decisive proof that quantum entanglement exists," Rosenbluh concludes.
"The proofs exist, even though this phenomenon challenges our fundamental assumptions. There is nothing that we don't know about the behavior of particles that can explain it. We know exactly how the particles behave; we simple don't understand how it can be," adds Dalla Torre. Rosenbluh says, "The contradiction is probably not in physics; it's in the way we understand the world."
"Globes": So if I move a cup of water, it will affect another cup of water in the world, because they both have quanta?
Rosenbluh: "This won't happen. In the visible world, in the sizes we experience with our senses, we won't see such phenomena. In the very small world, however, this is exactly what happens."
From what size exactly does this happen, and from what size does it stop happening, and why?
Pe'er: "This is one of the things we're trying to find out.
Rosenbluh: "One of the center's research questions is whether it is possible to make slightly larger particles perform quantum phenomena, and if it's at all practical. Professor Khaykovich, our partner in the center, has managed to demonstrate quantum phenomena in a group of 1,000 atomic particles under cold conditions - a millionth of a degree above absolute zero. Another researcher overseas has demonstrated quantum entanglement between atoms - a larger size than the one at which it was thought that quantum phenomena occur. What size can be reached? We don't know yet."
Is someone listening to you?
Scientists, however, are not waiting until it is discovered why quanta behave in this manner; they are already trying to find uses for the phenomenon. In addition to being further proof that modern physicists have not gone off their rockers, the various uses of the quantum entanglement phenomenon are opening new technological doors for applications that were previous impossible. One of these uses is called "quantum communications" or "quantum encryption." "Let's say that we want to transmit encrypted information," Pe'er explains. "First of all, we have to transfer the encryption key. If we have managed to transfer it, and we know definitely that no one listened to us, that's great. Now we are free to transmit all the information we want. But how will we know whether someone was listening to us? This, he says, is where the principles of quantum entanglement come in.
"Assume that we are splitting a stream of particles containing information and sending half of the stream to someone else, whom we will call Yossi Levy for the sake of the example (we keep the other half with us). Yossi decides by himself how to measure the stream of particles we sent to him, but the way he measures them retrospectively affects the particles that we have kept, because every particle reaching Yossi affects a particle left behind. After he finishes measuring all the particles, Yossi calls us and tells us exactly how he measured them and the result he got. We check our particles, and should get the complementary result, unless someone was listening to us. Such a third person couldn't know in advance how Yossi would decide to measure the particles, and what we see in our particles is therefore an effect of two measurements. That's how we know that someone's listening to us."
"Today's encryption is based on being hard to decode," Rosenbluh says. "You encrypt, and hope that the cipher is difficult to solve. If you have managed to transfer it without being listened to, however, you definitely know it. If you know that they're listening to you, you throw away this information and the entire communications channel."
Is this in use now?
Pe'er: "Yes - it's called quantum key distribution, and its use is just beginning."
Rosenbluh: "The Chinese recently reported that they transmitted quantum encrypted information via satellite for the first time."
Pe'er: "It's obviously a capability that all the strong players want: governments, banks, and corporation. Where does the problem lie? In the speed. Because one particle passes each time, and because a large proportion of the data is thrown away, speeds are low. Today, a speed of one megabyte per second is considered low, and when this method is used, you get at most one kilobyte per second. The speed falls when the distance increases. So the question is how can quantum information be transmitted at a normal speed, and we have a trick for it."
Rosenbluh: "In effect, the Bar Ilan center is developing the bandwidth of quantum communications. We are succeeding in running a broad spectrum of colors simultaneously between two offices, and instead of one photon, we run 10,000 photons, each with a different color."
Pe'er: "The big question is how you read 10,000 data simultaneously without needing 10,000 detectors. The answer also involves the quantum entanglement effect. Instead of splitting two particles each time, we split many particles. When they reach the destination, and provided that no one has overheard them, they should all converge to a single complete and predictable result. If that really happens, it means that no one was listening."
The quantum method of detecting terror tunnels
The quantum entanglement phenomenon makes it possible to take very precise measurements, and this is important in many other areas, for example in imaging tests, such as ultrasound or MRI, or in sonar measurements designed to detect whether there is oil or terror tunnels. As of now, this can be guessed, but not known for certain until a hole is drilled in the earth. How do quanta help us? Pe'er explains, "If I have two photon packets that should be the same, and after I pass one of them through specific material, there is a difference between the photons of the two packets, it's obvious that the difference is due to the effect of the material through which I passed the packet." Dalla Torre adds, "In the quantum world, there is the uncertainty principle, according to which if you know the location, you can never know the speed, but if you know the speed, you can't know the location. In quantum measurement, we put all the 'noise' on what's unimportant to us. If it's important for us to know the location, we measure so that the uncertainty will be on the speed side. If you know how many photons passed, you won't know the color, and if you decided to know what the color is, you won't know how many. Pe'er says, "Quantum uncertainty was always something disturbing, that added noise, and with the help of the quantum entanglement principle, we overcame this. We are already cooperating with defense companies.
Making the egg whole again
Another of the center's applications is quantum computing. Pe'er explains, "A conventional computer is made of transistors - electrical units that have two states: off and on. Quantum particles can contain information about more than two states. Assume that we have split a quantum-sized particle into 1,000 sub-particles and assigned each one a computational task. When it reaches a result, it affects all the others because of the principle of quantum entanglement principle. If I measure the result of all the particles simultaneously, I can quickly know how the state of each one has changed, because each one of them determined the final result. Analysis of this obviously requires a complex algorithm that Google, IBM, and Facebook are all working on. They all want to create quantum computing algorithms.
"Quantum computers have attracted great interest ever since they managed to perform a task that took conventional computer a long time to perform: to factor a large number into prime numbers. This is such a difficult talk that that many encryption codes have been based on it. The quantum computer can do it faster, because it can test several possibilities simultaneously. The problem now is that they haven't managed to produce it at the practical level. The most complex quantum computer today has a 16-bit memory."
According to the QUEST scientists, there is actually only one quantum computer in the world today, built by IBM in the US and located in the company's cellars. Next Wednesday, a company representative will visit Israel and explain how this computer can be accessed remotely and used from Israel. Note, however, that the world's first quantum computer can count only up to 256, so it is in effect useless. If its power is multiplied by 10, however, it can be used for computations that cannot be performed on an ordinary computer. If its power is multiplied by 100, there is a chance that someone could break into an email and read this article even before it is published. Stern is working on building a small quantum computer in his laboratory.
What are the challenges in building a quantum computer?
Rosenbluh: "One is not to lose the entanglement, because with time, the particles lose this connection with each other. The second is to maintain stability over time, because we do want it to be a computer with memory, not just the ability to perform short-lived calculations. Stern, one of the researchers at QUEST, is trying to connect the two components: one is static memory and the other is a quantum computer."
Dalla Torre: "What he actually has to do is entangle two different quantum systems – a conducting circuit above and an isolated atom. It's one level higher than entanglement of two identical particles."
Can you put a broken egg back together?
Do you believe that one day, we will succeed in creating a situation in which objects in different places affect each other in real time, including in the microscopic world? More importantly, can we change the direction of time?
Rosenbluh: "No one really knows why time goes in only direction in the world we know. Some say that the world was created with minimal entropy, and as entropy increases, this is something that is irreversible. For example, you can break a whole egg, but a broken egg never returns to its previous state by itself, and that is what makes time and cause and effect one-directional. But I don't think that this is the real explanation. In any case, in the quantum world, this phenomenon does not exist so clearly. 'Broken' things can be 'connected' as if they hadn't been broken. There are symmetrical phenomena, and entropy doesn't necessarily accumulate. You could say that in the nanoscopic world, time has no direction."
Can these phenomena be moved to the level of classical physics? Please hurry up, though, we are getting older here.
Pe'er: "There are probably fundamental reasons why it's impossible to bring the lack of direction in time to the classical physical world. In order for quantum symmetry to be preserved, you have to be able to follow every part of the results, and to make sure that nothing you don't know happens to any of them. An isolated quantum system is really symmetric with respect to time, but as soon as there is contact with the external world, and it always happens at some point, an element of uncertainty enters, and the process can no longer be reversed – the broken egg can't be made whole again."
Dalla Torre: "And systems that are so isolated are very inefficient."
Rosenbluh: "But that doesn't mean that people aren't working on this."
Published by Globes [online], Israel Business News - www.globes-online.com - on July 16, 2017
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