Probing quantum phenomena with near-term digital quantum simulation

A key feature distinguishing the quantum-mechanical realm from the classical one is the presence of quantum entanglement, which are correlations between degrees of freedom that escape classical description. It is therefore interesting to ask how entanglement can be manipulated, and more fundamentally, how entanglement behaves in a system undergoing some type of dynamics.

In the first part of this talk, I will discuss one of the first efforts in studying measurement-induced entanglement phase transitions on superconducting quantum processors [1]. In recent years deep theoretical evidence has amassed indicating that interspersing quantum measurements among ordinary unitary evolution can lead to a qualitatively different behavior of entanglement than unitary dynamics alone. In particular, as the rate of measurements cross a threshold, entanglement in the quantum system transitions from growing with the system volume (volume-law) to growing in proportion to cross-sectional area (area-law). By implementing hybrid random quantum circuits and exploiting mid-circuit readout, we directly observe this dynamical phase transition on up to 14 qubits. We also demonstrate criticality, in particular scale invariance characterized by critical exponents, near the phase transition point on hardware.

In the second part of this talk, I give a short overview of an array of recent work similarly leveraging quantum simulation on superconducting processors to probe condensed-matter systems. These include symmetry-protected topological phases in one spatial dimension [2], interacting Chern insulators hosting chiral modes in two dimensions [3], and higher-order topology in three or more dimensions [4].

While clear limitations remain in the near-term, in the longer term the versatility offered by digital quantum simulators in accessing broad classes of quantum systems and phenomena is incredibly exciting.

[1] Nat. Phys. 19, 1314–1319 (2023).

[2] npj Quantum Inf. 8, 16 (2022).

[3] Phys. Rev. Lett. 129, 140502 (2022).

[4] Nat. Commun. 15, 5807 (2024).