JQI-QuICS-CMTC Seminar

We study the connection between the charging power of a quantum battery and the fluctuations of the work stored in the battery. We show that in order to have a non-zero rate of change of the extractable work, the work fluctuations must be non-zero. This is presented in terms of an uncertainty relationship that bounds the speed of the charging process of any quantum system. Our findings also identify quantum coherence in the battery as a resource in the charging process, which we illustrate on a toy model of a heat engine.  

We show how to construct fully quantum multi-spin interactions using only two-body Ising interactions plus a uniform transverse field. We then provide an explicit embedding of simple gauge models, such as the surface code, into the D-Wave chimera architecture. Taken as whole this is a way to build topological qubits using existing hardware. The scheme is generalizable to other gauge-like theories, for example those with fractonic topological order such as the X-cube model.

Floquet engineering or coherent time periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to experimental realizations of artificial gauge fields, topological band structures, and observation of dynamical localization, to name just a few.

Strongly long-range interacting quantum systems---those with interactions decaying as a power-law 1/r^α in the distance r on a D-dimensional lattice for α ≤ D---have received significant interest in recent years. They are present in leading experimental platforms for quantum computation and simulation, as well as in theoretical models of quantum information scrambling and fast entanglement creation. Since no notion of locality is expected in such systems, a general understanding of their dynamics is lacking.

Quantized optical vortices, or the twisted photons, may carry pre-set amounts of angular momentum along their direction of propagation, thus allowing for quantum transitions otherwise forbidden for conventional plane-wave light. In this talk I will address the question of the angular momentum transfer to internal degrees of freedom of quantum systems excited by the twisted photons, and discuss appropriate polarization observables.

Future efforts to build quantum networks are likely to rely on the ability to interface and entangle disparate quantum systems. Two systems of interest in the realm of quantum information are trapped ions and Rydberg atoms. These systems operate at vastly different wavelengths so direct photonic interaction has been a challenge, however, establishing a photonic link would open the door to hybrid protocols leveraging the advantages of each system.

Product formulas (aka Trotterization) provide a straightforward yet surprisingly efficient approach to quantum simulation. We show that this algorithm can simulate an $n$-qubit Hamiltonian with nearest-neighbor interactions evolving for time $t$ using only $(nt)^{1+o(1)}$ gates. While it is reasonable to expect this complexity---in particular, this was claimed without rigorous justification by Jordan, Lee, and Preskill---we are not aware of a straightforward proof.

When one develops quantum information processors with larger numbers of qubits, correlated dephasing errors and crosstalk can have an important effect on the overall accuracy of the device. Detecting these correlations can require a large number of measurements. We consider the special case where the correlations are sparse, i.e., for a system of n qubits, there are k pairs of qubits that are correlated, where k << n(n-1)/2.

 Driving a conventional superconductor with an appropriately tuned classical electromagnetic field can lead to an enhancement of superconductivity via a redistribution of the quasiparticles into a more favorable non-equilibrium distribution – a phenomenon known as the Eliashberg effect. Here we theoretically consider coupling a two-dimensional superconducting film to the quantized electromagnetic modes of a microwave resonator cavity.

First there will be a discussion of quantum optics and the photon picture of light. Next, I will describe our four-wave mixing experiments in rubidium vapor cells and how we generate quantum light in the lab. The four-wave mixing process generates "twin beams" that exhibit squeezing and therefore entanglement that can be used for applications such as quantum communication and quantum imaging. Using a new technique, we recently demonstrated low frequency squeezing (< 10 Hz) which should make quantum imaging experiments feasible.