274 research outputs found
Design of nanophotonic circuits for autonomous subsystem quantum error correction
We reapply our approach to designing nanophotonic quantum memories to
formulate an optical network that autonomously protects a single logical qubit
against arbitrary single-qubit errors. Emulating the 9 qubit Bacon-Shor
subsystem code, the network replaces the traditionally discrete syndrome
measurement and correction steps by continuous, time-independent optical
interactions and coherent feedback of unitarily processed optical fields.Comment: 12 pages, 4 figure
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
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
Recurrence in generic staircases
The straight-line flow on almost every staircase and on almost every square
tiled staircase is recurrent. For almost every square tiled staircase the set
of periodic orbits is dense in the phase space
Triangulations and volume form on moduli spaces of flat surfaces
In this paper, we are interested in flat metric structures with conical
singularities on surfaces which are obtained by deforming translation surface
structures. The moduli space of such flat metric structures can be viewed as
some deformation of the moduli space of translation surfaces. Using geodesic
triangulations, we define a volume form on this moduli space, and show that, in
the well-known cases, this volume form agrees with usual ones, up to a
multiplicative constant.Comment: 42 page
Escape orbits and Ergodicity in Infinite Step Billiards
In a previous paper we defined a class of non-compact polygonal billiards,
the infinite step billiards: to a given decreasing sequence of non-negative
numbers , there corresponds a table \Bi := \bigcup_{n\in\N} [n,n+1]
\times [0,p_{n}].
In this article, first we generalize the main result of the previous paper to
a wider class of examples. That is, a.s. there is a unique escape orbit which
belongs to the alpha and omega-limit of every other trajectory. Then, following
a recent work of Troubetzkoy, we prove that generically these systems are
ergodic for almost all initial velocities, and the entropy with respect to a
wide class of ergodic measures is zero.Comment: 27 pages, 8 figure
Geometry, topology and dynamics of geodesic flows on noncompact polygonal surfaces
We establish the background for the study of geodesics on noncompact
polygonal surfaces. For illustration, we study the recurrence of geodesics on
-periodic polygonal surfaces. We prove, in particular, that almost all
geodesics on a topologically typical -periodic surface with boundary are
recurrent.Comment: 34 pages, 13 figures. To be published in V. V. Kozlov's Festschrif
Upgrading the Local Ergodic Theorem for planar semi-dispersing billiards
The Local Ergodic Theorem (also known as the `Fundamental Theorem') gives
sufficient conditions under which a phase point has an open neighborhood that
belongs (mod 0) to one ergodic component. This theorem is a key ingredient of
many proofs of ergodicity for billiards and, more generally, for smooth
hyperbolic maps with singularities. However the proof of that theorem relies
upon a delicate assumption (Chernov-Sinai Ansatz), which is difficult to check
for some physically relevant models, including gases of hard balls. Here we
give a proof of the Local Ergodic Theorem for two dimensional billiards without
using the Ansatz.Comment: 17 pages, 2 figure
Ergodicity of certain cocycles over certain interval exchanges
We show that for odd-valued piecewise-constant skew products over a certain
two parameter family of interval exchanges, the skew product is ergodic for a
full-measure choice of parameters
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