For sure, for most of our humanities readers, the meanings of the terms “quantum processor” or “qubit” still seem to be something from the realm of fantasy. But since the world is moving towards this particular type of computing, which, perhaps, will soon replace our usual “bit” computers, it is a little necessary to understand this difficult topic. Moreover, there is also an informational reason – the creation of the country’s first four-qubit processor based on superconductors.
Help “MK”. The computers that we now use everywhere use a bit as a unit of information (a signal that can take two values: on or off – 0 or 1). qubit – as a unit of information of a quantum computer (which can be a structure made of a superconducting metal deposited on a silicon wafer), can also be in position 0 or 1, but at the same time it can also be in their superposition (that is, be both zero and one at the same time ). Such a superposition allows a processor consisting of many qubits to perform parallel computations in the shortest possible time, several orders of magnitude greater than the capabilities of modern computers.
– Ilya, tell us what is the four-qubit processor that your team has assembled?
– Actually, there are five of them in our processor, but so far four of them have shown themselves in operation. Pure aluminum qubits (they are represented by crosses in the diagram) are deposited on a silicon wafer according to the corresponding pattern. This chip is installed in a special holder and works there if it is cooled to ultra-low temperatures, on the order of tens of millikelvins.
Why do they need to be at such a low temperature?
– Quantum information in qubits is very sensitive to thermal noise and electromagnetic interference. Elevated temperature and pollution near the qubit can very quickly lead to information loss. In order for it to work properly, the temperature near it must be close to absolute zero.
– Is that why scientists around the world are now competing to see who will have the longest qubit?
– Yes, including. The longer a qubit is able to store information, the fewer errors result from calculations. We are used to the fact that ordinary computers almost never make mistakes and work strictly in accordance with a given program, but a few decades ago this was not the case. So it is with quantum computers – the higher the reliability of qubits, the more complex algorithms they will be able to perform.
Recently, my colleagues and I from MSTU im. Bauman assembled another, two-qubit processor, whose qubits had a lifetime of about 100 microseconds – this is comparable to American and Chinese superconducting quantum processors, which are considered the most advanced in the world.
– What is the trick here? Why are you still not among the leaders?
– Because besides life expectancy for a full-fledged computer, the number of qubits themselves is also important. For example, our long-lived processor lacks about 50-100 qubits.
– And the Americans and the Chinese – how much?
Google showed off a 72-qubit device this year, a group from China showed 66 qubits last year. More recently, IBM presented a 433-qubit processor, but detailed results have not yet been published.
– That is, ideally, it is necessary to increase both the lifetime and the number of qubits. What are you missing in order to do this?
“This is a very difficult engineering task, it is quite difficult to make sure that the control signal does exactly what is needed, and the qubits behave correctly. And as always, there is not enough hardware and time. Due to the fact that we have all the equipment for experiments – imported, we have to wait a long time for it from abroad in order to start developing programs and conducting experiments. During this time, our competitors are striding forward by leaps and bounds.
– What exactly do you need?
– In electronic lithographs, which draw the structure of a microcircuit on a silicon substrate, on which qubits are then deposited. They don’t do that in Russia. They also don’t make arbitrary waveform generators (AWGs), which are used to manipulate qubits. We have such people at MISIS, at Baumanka, at Moscow Institute of Physics and Technology, but one or two for the entire laboratory, which, alas, is not enough. The second important component is a set of necessary algorithms and programs for work. We can download the basic ones from open sources, but for the scientific component, each laboratory develops its own for the tasks to be solved.
– What problems do quantum physicists solve today?
– Since it has long been understood that it is difficult to place many qubits on one plate, the whole world is moving to vertically integrated multi-level microcircuits, the so-called flip chips, in which dozens of qubits are combined.
– Tell me, do you have a guiding dream? What would you personally like to achieve to the maximum in the field of quantum technologies?
– Probably it will sound trite, but any person is happy when he likes what he is doing. The same applies to me – every day in the laboratory we solve interesting problems, we try to figure out how nature works, and I’m not only talking about working hours, but also on the way home, and sometimes on weekends, if you need to check new idea. A long-term dream now can be called a quantum computer with a processor of a thousand qubits and with an implemented program for correcting possible errors so that data is not lost. Such a system will be able to simulate the most complex processes of chemistry, will allow the development of new materials, new drugs, etc.
Will this computer be similar in appearance to the one we use now?
– The display may not change, but the prefix to it will definitely look different. Relatively speaking, it will be an ordinary desktop, and next to it is a room in which there is a powerful cryostat for constant cooling of qubits and a whole control system for generating and processing analog signals.
– In how many years can a thousand-qubit quantum computer appear?
– I hope that it will be implemented in the next decade.
Source From: MK