64 research outputs found
Role of thermal noise in tripartite quantum steering
The influence of thermal noise on bipartite and tripartite quantum steering
induced by a short laser pulse in a hybrid three-mode optomechanical system is
investigated. The calculation is carried out under the bad cavity limit, the
adiabatic approximation of a slowly varying amplitude of the cavity mode, and
with the assumption of driving the cavity mode with a blue detuned strong laser
pulse. Under such conditions, explicit expressions of the bipartite and
tripartite steering parameters are obtained, and the concept of collective
tripartite quantum steering, recently introduced by He and Reid [Phys. Rev.
Lett. 111, 250403 (2013)], is clearly explored. It is found that both bipartite
and tripartite steering parameters are sensitive functions of the initial state
of the modes and distinctly different steering behaviour could be observed
depending on whether the modes were initially in a thermal state or not. We
find that the initial thermal noise is more effective in destroying the
bipartite rather than the tripartite steering which, on the other hand, can
persist even for a large thermal noise. For the initial vacuum state of a
steered mode, the tripartite steering exists over the entire interaction time
even if the steering modes are in very noisy thermal states. When the steered
mode is initially in a thermal state, it can be collectively steered by the
other modes. There are thresholds for the average number of the thermal photons
above which the existing tripartite steering appears as the collective
steering. Finally, we point out that the collective steering may provide a
resource in a hybrid quantum network for quantum secret sharing protocol.Comment: 13 pages, 9 figure
Engineering asymmetric steady-state Einstein-Podolsky-Rosen steering in macroscopic hybrid systems
Generation of quantum correlations between separate objects is of
significance both in fundamental physics and in quantum networks. One important
challenge is to create the directional "spooky action-at-a-distanc" effects
that Schr\"{o}dinger called "steering" between two macroscopic and massive
objects. Here, we analyze a generic scheme for generating steering correlations
in cascaded hybrid systems in which two distant oscillators with effective
masses of opposite signs are coupled to a unidirectional light field, a setup
which is known to build up quantum correlations by means of quantum back-action
evasion. The unidirectional coupling of the first to the second oscillator via
the light field can be engineered to enhance steering in both directions and
provides an active method for controlling the asymmetry of steering. We show
that the resulting scheme can efficiently generate unconditional steady-state
Einstein-Podolsky-Rosen steering between the two subsystems, even in the
presence of thermal noise and optical losses. As a scenario of particular
technological interest in quantum networks, we use our scheme to engineer
enhanced steering from an untrusted node with limited tunability (in terms of
interaction strength and type with the light field) to a trusted, highly
tunable node, hence offering a path to implementing one-sided
device-independent quantum tasks.Comment: 11 pages, 8 figure
Number-phase entanglement and Einstein-Podolsky-Rosen steering
We use the uncertainty relation between the operators associated to the total
number of particles and to the relative phase of two bosonic modes to construct
entanglement and Einstein-Podolsky-Rosen steering criteria. These can be tested
experimentally in a variety of systems, such as optical fields, Bose-Einstein
condensates or mechanical oscillators. While known entanglement criteria
involving the phase observable typically require to perform interference
measurements by recombining the two systems, our criteria can be tested through
local measurements at two spatially distinct positions, to investigate the
nonlocal nature of quantum correlations. We present simple examples where our
criteria are violated, and show their robustness to noise. Apart from being
useful for state characterization, they might find application in quantum
information protocols, for example based on number-phase teleportation.Comment: Comments are welcome
Quantum Noise of Kramers-Kronig Receiver
Abstrac--Kramers-Kronig (KK) receiver, which is equivalent to heterodyne
detection with one single photodetector, provides an efficient method to
reconstruct the complex-valued optical field by means of intensity detection
given a minimum-phase signal. In this paper, quantum noise of the KK receiver
is derived analytically and compared with that of the balanced heterodyne
detection. We show that the quantum noise of the KK receiver keeps the radical
fluctuation of the measured signal the same as that of the balanced heterodyne
detection, while compressing the tangential noise to 1/3 times the radical one
using the information provided by the Hilbert transform. In consequence, the KK
receiver has 3/2 times the signal-to-noise ratio of balanced heterodyne
detection while presenting an asymmetric distribution of fluctuations, which is
also different from that of the latter. More interestingly, the projected
in-phase and quadrature field operators of the retrieved signal after down
conversion have a time dependent quantum noise distribution depending on the
time-varying phase. This property provides a feasible scheme for controlling
the fluctuation distribution according to the requirements of measurement
accuracy in the specific direction. Under the condition of strong carrier wave,
the fluctuations of the component requiring to be measured more accurately can
be compressed to 1 / 6, which is even lower than 1/4 by measuring a coherent
state. Finally, we prove the analytic conclusions by simulation results
Unconditional steady-state entanglement in macroscopic hybrid systems by coherent noise cancellation
The generation of entanglement between disparate physical objects is a key
ingredient in the field of quantum technologies, since they can have different
functionalities in a quantum network. Here we propose and analyze a generic
approach to steady-state entanglement generation between two oscillators with
different temperatures and decoherence properties coupled in cascade to a
common unidirectional light field. The scheme is based on a combination of
coherent noise cancellation and dynamical cooling techniques for two
oscillators with effective masses of opposite signs, such as quasi-spin and
motional degrees of freedom, respectively. The interference effect provided by
the cascaded setup can be tuned to implement additional noise cancellation
leading to improved entanglement even in the presence of a hot thermal
environment. The unconditional entanglement generation is advantageous since it
provides a ready-to-use quantum resource. Remarkably, by comparing to the
conditional entanglement achievable in the dynamically stable regime, we find
our unconditional scheme to deliver a virtually identical performance when
operated optimally.Comment: Final version; 6 pages, 3 figures + Supplemental Materia
Generating optical cat states via quantum interference of multi-path free-electron-photons interactions
The novel quantum effects induced by the free-electron-photons interaction
have attracted increasing interest due to their potential applications in
ultrafast quantum information processing. Here, we propose a scheme to generate
optical cat states based on the quantum interference of multi-path
free-electron-photons interactions that take place simultaneously with strong
coupling strength. By performing a projection measurement on the electron, the
state of light changes significantly from a coherent state into a non-Gaussian
state with either Wigner negativity or squeezing property, both possess
metrological power to achieve quantum advantage. More importantly, we show that
the Wigner negativity oscillates with the coupling strength, and the optical
cat states are successfully generated with high fidelity at all the oscillation
peaks. This oscillation reveals the quantum interference effect of the multiple
quantum pathways in the interaction of the electron with photons, by that
various nonclassical states of light are promising to be fast prepared and
manipulated. These findings inspire further exploration of emergent quantum
phenomena and advanced quantum technologies with free electrons
Auditory Attention Decoding with Task-Related Multi-View Contrastive Learning
The human brain can easily focus on one speaker and suppress others in
scenarios such as a cocktail party. Recently, researchers found that auditory
attention can be decoded from the electroencephalogram (EEG) data. However,
most existing deep learning methods are difficult to use prior knowledge of
different views (that is attended speech and EEG are task-related views) and
extract an unsatisfactory representation. Inspired by Broadbent's filter model,
we decode auditory attention in a multi-view paradigm and extract the most
relevant and important information utilizing the missing view. Specifically, we
propose an auditory attention decoding (AAD) method based on multi-view VAE
with task-related multi-view contrastive (TMC) learning. Employing TMC learning
in multi-view VAE can utilize the missing view to accumulate prior knowledge of
different views into the fusion of representation, and extract the approximate
task-related representation. We examine our method on two popular AAD datasets,
and demonstrate the superiority of our method by comparing it to the
state-of-the-art method
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