Topological bosonic states via squeezing

There is enormous interest in engineering topological photonic systems, where topological protection guarantees the existence of robust edge modes. Most works in this field amount to replicating a well-known fermionic single-particle Hamiltonian. We recently studied a class of systems where this correspondence fails. Here, topology is induced by coherent two-photon driving (i.e. parametric driving). While these systems have a Hamiltonian resembling that of a fermionic topological superconductor, the bosonic physics is completely different. In particular, the topologically-protected edge states can act as frequency-converting channels, and can even serve as quantum-limited amplifiers and squeezed light sources. It is even possible to construct bosonic systems that are reminiscent of the fermionic Kitaev-Majorana chain.

Nature Communications, 2016

Phys. Rev. X, 2016

Phys. Rev. X, 2018

Phys. Rev. B, 2021

Enhanced quantum sensing using quantum quenches

Some of the most common quantum sensing protocols exploit the dephasing of a probe qubit to study a a system of interest. Our work shows these methods can be made more powerful by making use of a quantum quench that is inadvertently induced on the probed system as part of standard protocols. These methods give rise to anomalous qubit phase shifts, which can be directly used to extract spectral functions of the probed system. This allows a parameter free measurement of temperature, and even the detection of non-thermal equilibrium states. These ideas are applicable to a range of sensing platforms, including nitrogen-vacancy (NV) centers in diamond and superconducting circuits.

Nature Commun., 2021