The first time crystal two-level system will lead to better quantum computers

Quantum computing has the potential to solve real-world problems that cannot be solved by today's classical computers. Unfortunately, however, it is fragile. Mainly affected by something called "decoherence," which is a lot like entropy. Time crystals may be able to solve this problem.

In May 2018, research from Aalto University in Finland suggested that time crystals may hold the key to making quantum computers. Through the process of self-oscillation, the time crystal exchanges electrons within itself without using energy, which allows the ions to remain coherent no matter how much time passes. In a paper published in the journal Nature Materials in August 2020, researchers observed the interaction of time crystals for the first time.

Now, physicists have created the first-ever time-crystal two-level system.

An international research team led by physicist Samuli Autti of Lancaster University in the UK successfully created two time crystals inside a superfluid and brought them into contact with each other, creating a coupled system that obeys quantum rules. Quantum computers run by qubits laid the groundwork.

The research results were published in the journal Nature Communications on June 2 under the title "Nonlinear Two-Level Dynamics of Quantum Time Crystals" [1].

Time crystals have long been thought impossible -- because they're made of "atoms" whose motions never end.

Time crystals are time analogues of ordinary crystals.

Time crystals are similar to ordinary crystals in that they are based on repeating atomic structures; however, the "atoms" of time crystals behave slightly differently: they exhibit patterns of motion in time that cannot be easily explained by external forces, These oscillations are locked to regular and specific frequencies. In theory, time crystals oscillate in the lowest possible energy state and are therefore stable and coherent over long periods of time; therefore, time crystals exhibit permanent ground-state motion as they repeat in space and time.

In 2012, Nobel laureate Frank Wilczek first proposed the theory of "time crystals". He proposes that even at the lowest energies, atoms may change over time, just as superconductors can technically carry electrical current at the lowest energy states. This means that, in theory, they could repeat forever without a source of energy, like a "perpetual motion machine"; but according to the laws of thermodynamics, such a device is impossible.

Frank Wilczek

Since Wilczek's prediction, many researchers have conducted experiments showing how atoms behave in ways that might qualify as time crystals.

In 2016, a team from the University of Maryland and Harvard University used a method proposed by researchers at the University of California, Berkeley, to formally discover and confirm time crystals [2]: Although there is no external input, these crystals exhibit constant, repetitive motion in time. Properties, their atoms constantly oscillate, spin, or move first in one direction and then in the other.

In 2020, the interaction of two quantum time crystals was realized for the first time, and it was shown that time crystals obey the rules of quantum mechanics [3].

The findings are significant: For the first time, isolated swarms of particles have manifested as exotic states of matter in time crystals and are connected to a single, evolving system, the next step in using time crystals for practical purposes , such as quantum information processing .

"Everyone knows that perpetual motion machines are impossible," Samuli Autti said. "However, in quantum physics, perpetual motion machines are possible as long as we close our eyes. By diving into this gap, we can make time crystals."

The time crystals used by the team consisted of quasiparticles called "magnons": magnons are not true particles, but consist of collective excitations of electron spins, like waves propagating through a spin lattice . When helium-3, a stable isotope of helium that has two protons but only one neutron, cools to within 1/10,000th of absolute zero, magnons appear — creating a "B-phase superfluid" ” (B-phase superfluid, an inviscid fluid with low pressure).

Schematic diagram of the experiment. The superfluid helium-3 sample was contained in a quartz glass cylinder. The magnon time crystal (blue sphere) is trapped in the middle of the container due to the minimum value of the static magnetic field and the spatial distribution of the superfluid orbital momentum L (small green arrow) using a pinch coil (green wire loop) The result of the combined action; coherent interplay of the magnetization M (pink cone) in the time crystal can be observed using a coil (NMR coil) ); the direction of the static magnetic field H is parallel to the axis of the cylinder.

In a medium such as a B-phase superfluid, time crystals form as spatially distinct Bose-Einstein condensates (formed by bosons cooled above absolute zero), each condensed by a trillion magnons Quasiparticle composition.

This causes them to sink into their lowest energy states, move very slowly and clump together and even overlap to create dense clouds of atoms that act like a "super atom" or matter wave. When the two time crystals were allowed to touch each other, they exchanged magnons. This exchange affects the oscillation of each time crystal, creating a single system where the time crystal can choose to operate in two discrete states.

The distribution of aL (green arrows) confines the magnon to two local minima, hosting two adjacent time crystals: one in the bulk of the superfluid (blue sphere) and the other touching the free surface (red sphere) . In each time crystal, the magnetization is coherent and coupled to the measurement circuit; b. the magnons change the confinement traps created by the L-distribution, which increases the coupling between states; c. the states of the two-level system ( red arrow) can be illustrated with a Bloch sphere, where the radial distance corresponds to the number of magnetons NB+NS, the relative phase between the rehearsals of the time crystal corresponds to the azimuth angle j, and the polar angle θ describes the "superposition" The relative weights of the two-level base states in the middle.

In quantum physics, objects can have multiple states and exist in a mixture of these states before being fixed by an unambiguous measurement. Therefore, having time crystals work in two-state systems offers a wealth of new options for quantum technology.

"It turns out that putting two time crystals together works well," explains Dr. Samuli Autti [4].

The basic building block of a quantum computer is called a "two-level system" - a quantum system that exists in a superposition of two independent quantum states. That's exactly what the researchers built this time, "in our experiments, two coupled time crystals consisting of spin-wave quasiparticles ... form a macroscopic two-level system," the paper explains.

"The evolution of these two energy levels over time is essentially determined by nonlinear feedback, allowing us to construct spontaneous two-level dynamics. Magnon time crystals allow understanding of the individual aspects of quantum coherent interactions in a single experiment. Aspects and details, so the discovery of this two-level system may provide a way to make quantum computers that work without cooling. "

Reference link:

[1] https://www.nature.com/articles/s41467-022-30783-w

[2] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.030401

[3] https://www.nature.com/articles/s41563-020-0780-y

[4] https://www.iflscience.com/physics/impossible-time-crystal-system-could-hold-secret-to-quantum-computing-revolution/