Google’s quantum computer has been used to build a “time crystal” according to freshly-published research, a new phase of matter that upends the traditional laws of thermodynamics. Despite what the name might suggest, however, the new breakthrough won’t let Google build a time machine.
Time crystals were first proposed in 2012, as systems that continuously operate out of equilibrium. Unlike other phases of matter, which are in thermal equilibrium, time crystals are stable yet the atoms which make them up are constantly evolving.
At least, that’s been the theory: scientists have disagreed on whether such a thing was actually possible in reality. Different levels of time crystals that could or could not be generated have been argued, with demonstrations of some that partly – but not completely – meet all the relevant criteria. In a new research preprint by researchers at Google, along with physicists at Princeton, Stanford, and other universities, it’s claimed that Google’s quantum computer project has delivered what many believed impossible. Preprints are versions of academic papers that are published prior to going through peer-review and full publishing; as such, their findings can be challenged or even overturned completely during that review process.
“Our work employs a time-reversal protocol that discriminates external decoherence from intrinsic thermalization, and leverages quantum typicality to circumvent the exponential cost of densely sampling the eigenspectrum,” the paper suggests. “In addition, we locate the phase transition out of the DTC with an experimental finite-size analysis. These results establish a scalable approach to study non-equilibrium phases of matter on current quantum processors.”
If that has gone right over your head, you’re probably not alone. As Quanta Magazine explains it, the time crystal basically consists of three core elements. First, a row of particles each with its own magnetic orientation gets locked into a mixture of low- and higher-energy configurations. That’s what’s known as a “many-body localization.”
Flipping all of the orientations of those particles – effectively creating a mirror version – is known as eigenstate order. It’s effectively a secondary many-body localized state.
Finally, there’s the application of laser light. That causes the states to cycle – from normal to mirrored, and then back again – but without actually using net energy from the laser itself. The result is known as a Floquet time crystal, first proposed in 2016.
Google’s quantum computer – known as Sycamore – was able to use a chip with 20 of its qubits, or controllable quantum particles, each of which can maintain two states simultaneously. By tuning the interaction strength between the individual quibits, the researchers could randomize the interactions and achieve many-body localization. Microwaves then upended the particles into their mirror orientation, but without the spin change taking net energy from that laser itself.
Where exactly that leaves both the theoretical research and the possible applications of a time crystal remains unclear. Right now, the main implication according to the researchers is that there’s “a scalable approach to study non-equilibrium phases of matter on current quantum processors”; in short, it demonstrates that quantum computers could at least be good for this line of work.
Figuring out a practical application for quantum computers and the reams of theory that come with them has been a common issue for companies digging into the technology. Earlier this year, Google made some bold predictions about just what its quantum project could achieve, pointing to improving batteries, making more effective drugs and vaccines, and generating more effective fertilizers as possible outcomes from such research. As part of that, the company says it is working on a 1,000,000 physical qubit quantum computer, though conceded it would take years before even understanding how that might be constructed could be figured out.