The realization of measurement induced quantum phases on a trapped-ion quantum computer

Ingrid Fadelli is a writer for the website Phys.org.

A trapped-ion quantum computer is a device that vibrates together and is completely isolated from the outside world. The computers can be used to investigate and realize quantum physics states.

Researchers at NIST/University of Maryland and Duke University have recently used a trapped-ion quantum computer to realize two measurement-induced quantum phases. Their findings contributed to the understanding of many-body quantum systems.

Crystal Noel is one of the researchers who carried out the study. The main goal of the paper was to use a quantum computer to observe the phenomenon.

The researchers had to average data collected over a number of random circuits to measure the purification phase transition. They collected both unitary and projective measures.

"If you start in a mixed state with information and then evolve the circuits, the end of the circuit will tell you if the system has been regenerated or if it has been lost," Noel said. After the evolution of the circuit, we measured the system's entropy.

The purification phase transition probed by the team should have emerged at a critical point, similar to a fault tolerant threshold. Noel and her colleagues used random circuits that were designed to work well with their ion trap quantum computer. They were able to see the different phases of purification using a relatively small system.

Noel said that critical phenomena of this nature are difficult to observe due to the need for large system sizes, mid-circuit measurement, and averaging over many random circuits taking significant computation time. We were able to modify the model we studied to the system we had available and show that the critical phenomena can still be observed.

The pure phase of the purification phase transition and the mixed phase were probed using the trapped-ion quantum computer. The system is projected to be a pure state in the first state. In the second, the system's initial state is converted into a quantum error correcting coding space, which keeps the system's memory of its original conditions.

Noel and her colleagues' success in realizing the two phases of the purification transition in their ion-trap quantum computer could inspire other teams to use similar systems to probe other quantum phases of matter. The same computer that was moved to the New Duke Quantum Center will continue to be used by the researchers. Chris Monroe, the principal investigator on the recent study, is now Director of this Center and will lead further studies using the trapped-ion quantum computer.

We plan to use our trapped ion quantum computer to study critical phenomena. More qubits and mid-circuit measurement will be added. We want to understand more about quantum computing and open quantum systems by finding new observables and interesting transitions that are similar to the one observed here.

More information: Crystal Noel et al, Measurement-induced quantum phases realized in a trapped-ion quantum computer, Nature Physics (2022). DOI: 10.1038/s41567-022-01619-7 Journal information: Nature Physics

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