645 research outputs found
Photon molecules in atomic gases trapped near photonic crystal waveguides
Realizing systems that support robust, controlled interactions between
individual photons is an exciting frontier of nonlinear optics. To this end,
one approach that has emerged recently is to leverage atomic interactions to
create strong and spatially non-local interactions between photons. In
particular, effective interactions have been successfully created via
interactions between atoms excited to Rydberg levels. Here, we investigate an
alternative approach, in which atomic interactions arise via their common
coupling to photonic crystal waveguides. This technique takes advantage of the
ability to separately tailor the strength and range of interactions via the
dispersion engineering of the structure itself, which can lead to qualitatively
new types of phenomena. As an example, we discuss the formation of correlated
transparency windows, in which photonic states of a certain number and shape
selectively propagate through the system. Through this technique, we show in
particular that one can create molecular-like potentials that lead to molecular
bound states of photon pairs
Entanglement Storage Units
We introduce a protocol based on optimal control to drive many body quantum
systems into long-lived entangled states, protected from decoherence by big
energy gaps, without requiring any apriori knowledge of the system. With this
approach it is possible to implement scalable entanglement-storage units. We
test the protocol in the Lipkin-Meshkov-Glick model, a prototype many-body
quantum system that describes different experimental setups, and in the ordered
Ising chain, a model representing a possible implementation of a quantum bus
Adiabatic quantum dynamics of the Lipkin-Meshkov-Glick model
The adiabatic quantum evolution of the Lipkin-Meshkov-Glick (LMG) model
across its quantum critical point is studied. The dynamics is realized by
linearly switching the transverse field from an initial large value towards
zero and considering different transition rates. We concentrate our attention
on the residual energy after the quench in order to estimate the level of
diabaticity of the evolution. We discuss a Landau-Zener approximation of the
finite size LMG model, that is successful in reproducing the behavior of the
residual energy as function of the transition rate in the most part of the
regimes considered. We also support our description through the analysis of the
entanglement entropy of the evolved state. The system proposed is a paradigm of
infinite-range interaction or high-dimensional models.Comment: 8 pages, 7 figures. (v2) minor revisions, published versio
Quantum Speed Limit and Optimal Control of Many-Boson Dynamics
We extend the concept of quantum speed limit -- the minimal time needed to
perform a driven evolution -- to complex interacting many-body systems. We
investigate a prototypical many-body system, a bosonic Josephson junction, at
increasing levels of complexity: (a) within the two-mode approximation
{corresponding to} a nonlinear two-level system, (b) at the mean-field level by
solving the nonlinear Gross-Pitaevskii equation in a double well potential, and
(c) at an exact many-body level by solving the time-dependent many-body
Schr\"odinger equation. We propose a control protocol to transfer atoms from
the ground state of a well to the ground state of the neighbouring well.
Furthermore, we show that the detrimental effects of the inter-particle
repulsion can be eliminated by means of a compensating control pulse, yielding,
quite surprisingly, an enhancement of the transfer speed because of the
particle interaction -- in contrast to the self-trapping scenario. Finally, we
perform numerical optimisations of both the nonlinear and the (exact) many-body
quantum dynamics in order to further enhance the transfer efficiency close to
the quantum speed limit.Comment: 5 pages, 3 figures, and supplemental material (4 pages 1 figure
Quantum dynamics of propagating photons with strong interactions: a generalized input-output formalism
There has been rapid development of systems that yield strong interactions
between freely propagating photons in one dimension via controlled coupling to
quantum emitters. This raises interesting possibilities such as quantum
information processing with photons or quantum many-body states of light, but
treating such systems generally remains a difficult task theoretically. Here,
we describe a novel technique in which the dynamics and correlations of a few
photons can be exactly calculated, based upon knowledge of the initial photonic
state and the solution of the reduced effective dynamics of the quantum
emitters alone. We show that this generalized "input-output" formalism allows
for a straightforward numerical implementation regardless of system details,
such as emitter positions, external driving, and level structure. As a specific
example, we apply our technique to show how atomic systems with infinite-range
interactions and under conditions of electromagnetically induced transparency
enable the selective transmission of correlated multi-photon states
Speeding up critical system dynamics through optimized evolution
The number of defects which are generated on crossing a quantum phase
transition can be minimized by choosing properly designed time-dependent
pulses. In this work we determine what are the ultimate limits of this
optimization. We discuss under which conditions the production of defects
across the phase transition is vanishing small. Furthermore we show that the
minimum time required to enter this regime is , where
is the minimum spectral gap, unveiling an intimate connection between
an optimized unitary dynamics and the intrinsic measure of the Hilbert space
for pure states. Surprisingly, the dynamics is non-adiabatic, this result can
be understood by assuming a simple two-level dynamics for the many-body system.
Finally we classify the possible dynamical regimes in terms of the action
.Comment: 6 pages, 6 figure
Recommended from our members
Noise-Resistant Optimal Spin Squeezing via Quantum Control
Entangled atomic states, such as spin squeezed states, represent a promising resource for a new generation of quantum sensors and atomic clocks. We demonstrate that optimal control techniques can be used to substantially enhance the degree of spin squeezing in strongly interacting many-body systems, even in the presence of noise and imperfections. Specifically, we present a time-optimal protocol that yields more than two orders of magnitude improvement with respect to conventional adiabatic preparation. Potential experimental implementations are discussed.Physic
Chopped random-basis quantum optimization
In this work we describe in detail the "Chopped RAndom Basis" (CRAB) optimal
control technique recently introduced to optimize t-DMRG simulations
[arXiv:1003.3750]. Here we study the efficiency of this control technique in
optimizing different quantum processes and we show that in the considered cases
we obtain results equivalent to those obtained via different optimal control
methods while using less resources. We propose the CRAB optimization as a
general and versatile optimal control technique.Comment: 9 pages, 10 figure
Noise-resistant optimal spin squeezing via quantum control
Entangled atomic states, such as spin squeezed states, represent a promising
resource for a new generation of quantum sensors and atomic clocks. We
demonstrate that optimal control techniques can be used to substantially
enhance the degree of spin squeezing in strongly interacting many-body systems,
even in the presence of noise and imperfections. Specifically, we present a
protocol that is robust to noise which outperforms conventional methods.
Potential experimental implementations are discussed.Comment: 5 pages of main tex
- âŠ