808 research outputs found
Loops and Strings in a Superconducting Lattice Gauge Simulator
We propose an architecture for an analog quantum simulator of
electromagnetism in 2+1 dimensions, based on an array of superconducting
fluxonium devices. The encoding is in the integer (spin-1 representation of the
quantum link model formulation of compact U(1) lattice gauge theory. We show
how to engineer Gauss' law via an ancilla mediated gadget construction, and how
to tune between the strongly coupled and intermediately coupled regimes. The
witnesses to the existence of the predicted confining phase of the model are
provided by nonlocal order parameters from Wilson loops and disorder parameters
from 't Hooft strings. We show how to construct such operators in this model
and how to measure them nondestructively via dispersive coupling of the
fluxonium islands to a microwave cavity mode. Numerical evidence is found for
the existence of the confined phase in the ground state of the simulation
Hamiltonian on a ladder geometry.Comment: 17 pages, 5 figures. Published versio
Non-absorbing high-efficiency counter for itinerant microwave photons
Detecting an itinerant microwave photon with high efficiency is an
outstanding problem in microwave photonics and its applications. We present a
scheme to detect an itinerant microwave photon in a transmission line via the
nonlinearity provided by a transmon in a driven microwave resonator. With a
single transmon we achieve 84% distinguishability between zero and one
microwave photons and 90% distinguishability with two cascaded transmons by
performing continuous measurements on the output field of the resonator. We
also show how the measurement diminishes coherence in the photon number basis
thereby illustrating a fundamental principle of quantum measurement: the higher
the measurement efficiency, the faster is the decoherence
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