Beyond Google! IBM quantum computer has produced the largest time crystal so far

Last year, the Google team announced the first use of quantum computers to create "time crystals", and research in this field has been out of control since then. Researchers from Norman Yao of the University of California, Berkeley and qutech in the Netherlands used a diamond quantum computer to make a "time crystal" that lasted about 8 seconds and lived 10 times longer than Google's experiment.

Now Philipp Frey and Stephan Rachel of the University of Melbourne School of physics have used IBM quantum computers to create the largest time crystal to date. Time crystal is a system composed of quantum particles. It is locked in a permanent cycle in time, which is a bit similar to the repeated space mode of atoms in ordinary crystals.

The new time crystal consists of 57 quantum particles, more than twice the 20 particle time crystal simulated by Google scientists last year. Chetan Nayak, a Microsoft condensed matter physicist who was not involved in the work, said the system was too large for traditional computers to simulate. "So this is definitely an important progress." This work shows the ability of quantum computers to simulate complex systems that might otherwise exist only in physicists' theories.

Realization principle of time crystal

The concept of time crystals emerged 10 years ago, When MIT Nobel laureate and theoretical physicist Frank Wilczek was inspired by the atomic space model of ordinary crystals. Where does this model come from? The equation of interatomic force does not specify this, which seems to allow any atom to appear anywhere with the same probability. On the contrary, if the atom cools sufficiently, it will appear spontaneously. Once several atoms are close to each other, the position of the next atom becomes predictable, and a mode hidden only in the force appears.

The concept of time crystals emerged 10 years ago, When MIT Nobel laureate and theoretical physicist Frank Wilczek was inspired by the atomic space model of ordinary crystals. Where does this model come from? The equation of interatomic force does not specify this, which seems to allow any atom to appear anywhere with the same probability. On the contrary, if the atom cools sufficiently, it will appear spontaneously. Once several atoms are close to each other, the position of the next atom becomes predictable, and a mode hidden only in the force appears.

The system consists of a series of tiny quantum-mechanical magnets, which can point up, down, or in both directions at the same time. In the flux chain, adjacent magnets tend to be arranged in opposite directions to reduce energy, while randomly selected local magnetic fields tend to point each magnet in one or another direction. A steady magnetic pulse flow will also periodically flip the magnet, and vice versa.

The idea is that the magnet will flip twice under any condition. Experimenters have demonstrated this idea in various systems, from electrons in diamond to ions captured in wells to quantum bits in quantum computers.

Simulation using 57 qubits

In this work, Philipp Frey, a theorist at the University of Melbourne, and his graduate student Stephan Rachel used a quantum computer manufactured and operated by IBM to conduct a remote simulation.

According to the paper published in the progress of Science [1], qubits can be set to 0, 1, or 1 and 0 at a time and can be programmed to interact like magnets. The researchers found that for some settings of their interaction, any initial setting of 57 qubits (such as 01101110...) remained stable and returned to the original state every two pulses.

At first glance, this observation seems a bit disappointing. After all, if the magnets do not interact, each pulse flips them 180 degrees, producing exactly half the frequency response.

However, Dominic else, a condensed matter theorist at Harvard University, explained that what makes the system a time crystal is the way in which the interaction between magnets stabilizes the mode. This makes the system unaffected by defects, such as insufficient pulse length to flip. "This is actually a phase of matter, stabilized by multi-body interactions," else said.

However, it is not enough to only improve the intensity of magnet interaction. Rachel said that the interaction between each pair of adjacent magnets will also change randomly. If all magnets interact at the same strength, if one magnet goes wrong, it may cause other magnets in the flux chain to flip in the wrong way. This randomness actually prevents the propagation of this error and stabilizes the time crystal.

Although more than 100 researchers participated in Google simulation, Frey and Rachel conducted a larger demonstration alone and submitted it to IBM computer through the Internet. Rachel said, "it's just me, my graduate student and a laptop. Philipp is great!" He estimated that the whole project took about six months.

Rachel said the demonstration was not perfect. This flip mode should last indefinitely, but the time that a qubit in an IBM machine stays in state can only simulate about 50 cycles. Finally, the stabilization effect of the interaction may be used to store the state of a string of qubits in the memory of a quantum computer.

Link:

[1]https://www.science.org/doi/10.1126/sciadv.abm7652

[2]https://www.science.org/content/article/physicists-produce-biggest-time-crystal-yet