31 research outputs found
The SLH framework for modeling quantum input-output networks
Many emerging quantum technologies demand precise engineering and control
over networks consisting of quantum mechanical degrees of freedom connected by
propagating electromagnetic fields, or quantum input-output networks. Here we
review recent progress in theory and experiment related to such quantum
input-output networks, with a focus on the SLH framework, a powerful modeling
framework for networked quantum systems that is naturally endowed with
properties such as modularity and hierarchy. We begin by explaining the
physical approximations required to represent any individual node of a network,
eg. atoms in cavity or a mechanical oscillator, and its coupling to quantum
fields by an operator triple . Then we explain how these nodes can be
composed into a network with arbitrary connectivity, including coherent
feedback channels, using algebraic rules, and how to derive the dynamics of
network components and output fields. The second part of the review discusses
several extensions to the basic SLH framework that expand its modeling
capabilities, and the prospects for modeling integrated implementations of
quantum input-output networks. In addition to summarizing major results and
recent literature, we discuss the potential applications and limitations of the
SLH framework and quantum input-output networks, with the intention of
providing context to a reader unfamiliar with the field.Comment: 60 pages, 14 figures. We are still interested in receiving
correction
A superconducting microwave multivibrator produced by coherent feedback
We investigate a coherent nonlinear feedback circuit constructed from
pre-existing superconducting microwave devices. The network exhibits emergent
bistable and astable states, and we demonstrate its operation as a latch and
the frequency locking of its oscillations. While the network is tedious to
model by hand, our observations agree quite well with the semiclassical
dynamical model produced by a new software package [N. Tezak et al.,
arXiv:1111.3081v1] that systematically interpreted an idealized schematic of
the system as a quantum optic feedback network.Comment: 9 double-spaced pages, 5 figures and supplement. To appear in Phys.
Rev. Let
Remnants of semiclassical bistability in the few-photon regime of cavity QED
Broadband homodyne detection of the light transmitted by a Fabry-Perot cavity
containing a strongly-coupled Cs atom is used to probe the dynamic
optical response in a regime where semiclassical theory predicts bistability
but strong quantum corrections should apply. While quantum fluctuations
destabilize true equilibrium bistability, our observations confirm the
existence of metastable states with finite lifetimes and a hysteretic response
is apparent when the optical drive is modulated on comparable timescales. Our
experiment elucidates remnant semiclassical behavior in the attojoule (
photon) regime of single-atom cavity QED, of potential significance for
ultra-low power photonic signal processing.Comment: 14 pages, 7 figure
An efficient all-optical switch using a lambda atom in a cavity QED system
We propose an all-optical switch constructed from a two-mode optical
resonator containing a strongly coupled, three-state system. The coupling
allows a weak, continuous wave laser drive to incoherently control the
transmission of a much stronger, continuous wave signal laser into (and
through) the resonator. We demonstrate that in this simple setup the presence
of a control drive with one tenth the power of the signal drive can induce near
complete reflection of the signal, while its absence allows for near complete
transmission. The switch can also be operated as a set-reset relay with two
control inputs that efficiently drive the switch into either the reflecting or
the transmitting state.Comment: 9 pages, 10 figures, v2: published versio
Tunable coupling to a mechanical oscillator circuit using a coherent feedback network
We demonstrate a fully cryogenic microwave feedback network composed of
modular superconducting devices connected by transmission lines and designed to
control a mechanical oscillator coupled to one of the devices. The network
features an electromechanical device and a tunable controller that coherently
receives, processes and feeds back continuous microwave signals that modify the
dynamics and readout of the mechanical state. While previous electromechanical
systems represent some compromise between efficient control and efficient
readout of the mechanical state, as set by the electromagnetic decay rate, the
tunable controller produces a closed-loop network that can be dynamically and
continuously tuned between both extremes much faster than the mechanical
response time. We demonstrate that the microwave decay rate may be modulated by
at least a factor of 10 at a rate greater than times the mechanical
response rate. The system is easy to build and suggests that some useful
functions may arise most naturally at the network-level of modular, quantum
electromagnetic devices.Comment: 11 pages, 6 figures, final published versio
Physical model of continuous two-qubit parity measurement in a cavity-QED network
We propose and analyze a physical implementation of two-qubit parity
measurements as required for continuous error correction, assuming a setup in
which the individual qubits are strongly coupled to separate optical cavities.
A single optical probe beam scatters sequentially from the two cavities and the
continuous parity measurement is realized via fixed quadrature homodyne
photo-detection. We present models based on quantum stochastic differential
equations (QSDE's) for both an ideal continuous parity measurement and our
proposed cavity quantum electrodynamics (cavity QED) implementation; a recent
adiabatic elimination theorem for QSDE's is used to assert strong convergence
of the latter to the former in an appropriate limit of physical parameters.
Performance of the cavity QED scheme is studied via numerical simulation with
experimentally realistic parameters.Comment: 4 pages, 3 figure
The dressed atom as binary phase modulator: towards attojoule/edge optical phase-shift keying
Nanophotonic technologies offer great promise for ultra-low power optical
signal processing, but relatively few nonlinear-optical phenomena have yet been
explored as bases for robust digital
modulation/switching~\cite{Yang07,Fara08,Liu10,Noza10}. Here we show that a
single two-level system (TLS) coupled strongly to an optical resonator can
impart binary phase modulation on a saturating probe beam. Our experiment
relies on spontaneous emission to induce occasional transitions between
positive and negative phase shifts---with each such edge corresponding to a
dissipated energy of just one photon ( aJ)---but an optical
control beam could be used to trigger additional phase switching at signalling
rates above this background. Although our ability to demonstrate controlled
switching in our atom-based experiment is limited, we discuss prospects for
exploiting analogous physics in a nanophotonic device incorporating a quantum
dot as the TLS to realize deterministic binary phase modulation with control
power in the aJ/edge regime.Comment: 7 pages, 4 figure