Sycamore (quantum computer)

Main article: Quantum Computer and Quantum Communication

2021: Time crystal with ordered eigenstates

On August 4, 2021, it became known that researchers from Google and several American universities reported the creation of a true discrete time crystal with ordered eigenstates. This state was obtained on the qubits of the quantum processor Sycamore from Google. Scientists have demonstrated that the time crystal they created meets a number of criteria that allow us to consider it a true time crystal. The preprint of the article is published on arXiv.org.

As explained, a time crystal is a hypothetical system whose characteristics periodically change over time even if it is in a basic energy state. This name was given looking at the usual crystals in which periodicity occurs in one or more spatial directions, and the crystals themselves form when the temperature of the medium decreases. However, almost immediately after the emergence, the idea of ​ ​ temporary crystals was criticized by physicists. The fact is that under thermodynamic equilibrium conditions, a system in a basic state cannot make any fluctuations. In the excited state, its evolution cannot be strictly periodic in time, as required by the concept of time crystals, due to the desire of the system to transition to the ground state.

However, scientists have found a way around this problem. It turned out that it is possible to ensure the stability of the system in an excited state if you prohibit it from relaxing into the ground state using the so-called multi-partial localization. This is a related effect to Anderson's localization, which keeps the particle system in a small area of ​ ​ space (real or phase) due to quantum interference of their wave functions in a disordered medium. The calculations of theorists have shown that by applying external periodic influence to a localized system, it is possible to cause fluctuations in it that will last as long as you like. This concept is called a discrete time crystal.

From that moment, reports periodically appeared in scientific journals that a particular group demonstrated a discrete time crystal. However, a number of physicists noticed that not all of them can be considered true time crystals, since sometimes systems are masked by their behavior, which, although slowly, strive for thermodynamic equilibrium, coming to it at a long time distance. In the end, several criteria were formulated that distinguish the true crystal of time from the apparent one, and the experimenters faced the task of creating a system that corresponds to them all.

In the work, participants in the Quantum Artificial Intelligence Lab collaboration, together with physicists from several American universities, with the participation of Roderich Moessner, director of the Max Planck Institute for Complex Systems Physics, Germany, presented the results of creating a discrete time crystal on 20 qubits of the Sycamore quantum processor created by Google. They showed that the system they constructed meets all the criteria formulated earlier and therefore can be considered a true discrete time crystal.

Their work is based on the idea of ​ ​ ordered eigenstates of a multi-partial-localized system. In general, when the system is periodically exposed, the range of its states may be erratic. When the states of the system are "frozen" by localization, their even superpositions line up in phase space exactly opposite their odd superpositions. When superimposed on such a periodic disturbance system, it can show a response with a doubled period for as long as desired. At the same time, energy is not dissipated and is not taken from the disturbing wave.

a) The energy levels of an arbitrary system in thermodynamic equilibrium, whose Hamiltonian does not depend on time. Long-range order is observed only in the main duplex (even and odd superposition). b) The disordered spectrum of a system whose Hamilnonian depends on time periodically. Quasi-energies are deposited on a circle of unit length. c) An ordered spectrum of a system whose Hamilnonian depends on time periodically. Even and odd superpositions of ordered states differ from each other by 180 degrees.

To realize this idea, physicists created chains of 20 transmon qubits of a quantum processor, the states of which they controlled using microwave radiation. An important possibility of such a system before analogues is that the force of interaction of qubits with the external field and with each other can be easily adjusted. This makes it possible to investigate the conditions under which the state of the time crystal arises and its stability by changing the parameters of the Ising model, which well describes such chains.

To confirm the truth of the manufactured temporary crystal, the authors needed to satisfy several criteria: the periodicity should be maintained when varying communication parameters in a certain range of parameters and when making a mess in the initial states; limitations on crystal size and coherence time should be expanded by increasing the number of qubits and separating the effects of decoherence from the effects of transition to an equilibrium state (thermalization); the entire spectrum of the time crystal must be ordered according to its own states.

Physicists conducted a series of measurements to prove that their installation meets all criteria. In particular, the temporal periodicity of qubit properties was investigated using autocorrelation functions, the introduction of disorder using a quantum scrambler, and the separation of decoherence from thermalization using an additional time-inverted effect on the system. Finally, scientists repeated their experiments for chains of 8, 12 and 16 qubits to make sure that the space-time constraints of the studied state increased. The latter, according to the authors, gives the basis for scaling true time crystals.

As of August 2021, it is not completely clear whether the true time crystal can find practical application. However, according to the authors, their result shows the conceptual possibility of the existence of a stable non-equilibrium phase. Ultimately, such studies provide an opportunity to look at the nature of space and time from a different angle. In addition, the creation of time crystals on quantum processors can become an additional motivation for the development of quantum computers^[1].

2019: Google has created the most powerful quantum computer in the world

In mid-September 2019, Google announced that it was able to create the world's most powerful quantum computer. Information about the device was published in a NASA report, which was subsequently removed from the organization's website.

The report said that Google has reached a milestone known as quantum superiority, since its quantum computer can be used to perform calculations that are not subject to other electronic systems.

Google announced that it was able to create the world's most powerful quantum computer

Google said that it was able to create a quantum processor that was able to make calculations in 3 minutes and 20 seconds that require about 10 thousand years of operation of IBM Summit's most modern supercomputer, the report said.

This hotly anticipated goal should mark the beginning of a new era of quantum computing. Although the text of the report disappeared from the NASA website, an article posted anonymously on the Pastebin website spread across the network. According to this version of the article, Google created a quantum computer called Sycamore with 54 quantum bits called qubits, 53 of which functioned.

A Google spokesman declined to comment at the request of the Financial Times. A company source familiar with the situation suggests that NASA accidentally published the report ahead of time before the conclusions contained in it were carefully checked by other scientists.

If the report passes the scientific test, a real revolution will occur in quantum science. Experts believe that with the advent of at least one real quantum computer, the power of new models will grow twice as fast as the exponential growth determined by Moore's law for traditional computing devices. However, the report said that the quantum computer is not yet ready to solve practical problems.^[2]

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