4,421 research outputs found
Enhancing quantum transduction via long-range waveguide mediated interactions between quantum emitters
Efficient transduction of electromagnetic signals between different frequency
scales is an essential ingredient for modern communication technologies as well
as for the emergent field of quantum information processing. Recent advances in
waveguide photonics have enabled a breakthrough in light-matter coupling, where
individual two-level emitters are strongly coupled to individual photons. Here
we propose a scheme which exploits this coupling to boost the performance of
transducers between low-frequency signals and optical fields operating at the
level of individual photons. Specifically, we demonstrate how to engineer the
interaction between quantum dots in waveguides to enable efficient transduction
of electric fields coupled to quantum dots. Owing to the scalability and
integrability of the solid-state platform, our transducer can potentially
become a key building block of a quantum internet node. To demonstrate this, we
show how it can be used as a coherent quantum interface between optical photons
and a two-level system like a superconducting qubit.Comment: The maintext has 6 pages, two column and 4 figure
Photon Scattering from a System of Multi-Level Quantum Emitters. I. Formalism
We introduce a formalism to solve the problem of photon scattering from a
system of multi-level quantum emitters. Our approach provides a direct solution
of the scattering dynamics. As such the formalism gives the scattered fields
amplitudes in the limit of a weak incident intensity. Our formalism is equipped
to treat both multi-emitter and multi-level emitter systems, and is applicable
to a plethora of photon scattering problems including conditional state
preparation by photo-detection. In this paper, we develop the general formalism
for an arbitrary geometry. In the following paper (part II), we reduce the
general photon scattering formalism to a form that is applicable to
-dimensional waveguides, and show its applicability by considering explicit
examples with various emitter configurations.Comment: This is first part of a two part series of papers. It has 11 pages,
double column, and one figur
Prediction of quantum stripe ordering in optical lattices
We predict the robust existence of a novel quantum orbital stripe order in
the -band Bose-Hubbard model of two-dimensional triangular optical lattices
with cold bosonic atoms. An orbital angular momentum moment is formed on each
site exhibiting a stripe order both in the superfluid and Mott-insulating
phases. The stripe order spontaneously breaks time-reversal, lattice
translation and rotation symmetries. In addition, it induces staggered
plaquette bond currents in the superfluid phase. Possible signatures of this
stripe order in the time of flight experiment are discussed.Comment: 4 pages, three figures, accepted by Phys. Rev. Let
Incommensurate superfluidity of bosons in a double-well optical lattice
We study bosons in the first excited Bloch band of a double-well optical
lattice, recently realized at NIST. By calculating the relevant parameters from
a realistic nonseparable lattice potential, we find that in the most favorable
cases the boson lifetime in the first excited band can be several orders of
magnitude longer than the typical nearest-neighbor tunnelling timescales, in
contrast to that of a simple single-well lattice. In addition, for sufficiently
small lattice depths the excited band has minima at nonzero momenta
incommensurate with the lattice period, which opens a possibility to realize an
exotic superfluid state that spontaneously breaks the time-reversal,
rotational, and translational symmetries. We discuss possible experimental
signatures of this novel state.Comment: 4 pages, 5 figures
Quantum Wire Network with Magnetic Flux
The charge transport and the noise of a quantum wire network, made of three
semi-infinite external leads attached to a ring crossed by a magnetic flux, are
investigated. The system is driven away from equilibrium by connecting the
external leads to heat reservoirs with different temperatures and/or chemical
potentials. The properties of the exact scattering matrix of this configuration
as a function of the momentum, the magnetic flux and the transmission along the
ring are explored. We derive the conductance and the noise, describing in
detail the role of the magnetic flux. In the case of weak coupling between the
ring and the reservoirs, a resonant tunneling effect is observed. We also
discover that a non-zero magnetic flux has a strong impact on the usual
Johnson-Nyquist law for the pure thermal noise at small temperatures.Comment: LaTex, 6 pages, 6 figures, improved discussion of the impact of the
magnetic flux on the pure thermal nois
A New Compact Delay, Doppler Stretch and Phase Estimation CRB with a Band-Limited Signal for Generic Remote Sensing Applications
Since time-delay, Doppler effect and phase estimation are fundamental tasks in a plethora
of engineering fields, tractable lower performance bounds for this problem are key tools of broad
interest for a large variety of remote sensing applications. In the large sample regime and/or the high
signal-to-noise ratio regime of the Gaussian conditional signal model, the Cramér–Rao bound (CRB)
provides an accurate lower bound in the mean square error sense. In this contribution, we introduce
firstly a new compact CRB expression for the joint time-delay and Doppler stretch estimation,
considering a generic delayed and dilated band-limited signal. This generalizes known results
for both wideband signals and the standard narrowband signal model where the Doppler effect
on the band-limited baseband signal is not considered and amounts to a frequency shift. General
compact closed-form CRB expressions for the amplitude and phase are also provided. These compact
CRBs are expressed in terms of the baseband signal samples, making them especially easy to use
whatever the baseband signal considered, therefore being valid for a variety of remote sensors.
The new CRB expressions are validated in a positioning case study, both using synthetic and real
data. These results show that the maximum likelihood estimator converges to the CRB at high
signal-to-noise ratios, which confirms the exactness of the CRB. The CRB is further validated by
comparing the ambiguity function and its 2nd order Taylor expansion where the perfect match also
proves its exactness
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