JQI

Abstract: Sampling from the output distributions of quantum computations comprising only commuting gates, known as instantaneous quantum polynomial (IQP) computations, is believed to be intractable for classical computers, and hence this task has become a leading candidate for testing the capabilities of quantum devices. Here we demonstrate that for an arbitrary IQP circuit undergoing dephasing or depolarizing noise, whose depth is greater than a critical O(1)threshold, the output distribution can be efficiently sampled by a classical computer.

Extensively degenerate ground-state spaces due to frustration pose a formidable resource for emergent quantum phenomena. Perturbing extensively degenerate ground-state spaces may result in several distinct scenarios lifting the ground-state degeneracy. First, an infinitesimal perturbation can lead to a symmetry-broken order (order-by-disorder) or second the perturbation can result in a symmetry-unbroken phase (disorder-by-disorder), which can be either trivial or an exotic quantum spin liquid.

There has been interest in the dynamics of noninteracting bosons because of the boson sampling problem. These dynamics can be difficult to predict because of the complicated interference patterns that arise due to their indistinguishability. However, if there are unobserved, hidden degrees of freedom, the indistinguishability can be disrupted in the observations. The generalized bunching probability is defined to be the probability that noninteracting bosons undergo linear optical evolution and all arrive in a subset of sites.

The main goal of quantum metrology is to leverage quantum mechanical objects such as atoms and molecules to improve sensing in any one of various aspects including sensitivity, speed, spatio-temporal resolution, and economic cost. A paradigmatic example is the use of entangled quantum particles to improve upon the standard quantum limit and achieve an improved sensitivity only limited by the Heisenberg uncertainty principle.

New techniques and resources in ultracold atomic physics have continually deepened its impact on science.  I will discuss two experimental developments that, hopefully, exemplify this trend.  First, I will share how my research group is using the versatile tool of atom-tweezer arrays to study collective atom-light coupling and symmetry-breaking in the mesoscopic regime.  Specifically, we show how, akin to the response of metamaterials, the precise control over the positions of atoms affects their collective coupling to an optical cavity.  This collective coupling t

Superconducting circuits provide a versatile platform for investigating many-body physics in synthetic quantum matter. Achieving scalable quantum simulation with these devices requires new methods for control and measurement. In this talk, I will present our recent experiments to control and probe quantum dynamics using both coherent and driven-dissipative techniques. First, I’ll discuss a set of transport experiments, where we develop an in-situ measurement of particle current and current statistics.