902 research outputs found
Constraints on the Bulk Lorentz Factors of GRB X-Ray Flares
X-ray flares were discovered in the afterglow phase of gamma-ray bursts
(GRBs) by the {\em Swift} satellite a decade ago and known as a canonical
component in GRB X-ray afterglows. In this paper, we constrain the Lorentz
factors of GRB X-ray flares using two different methods. For the first method,
we estimate the lower limit on the bulk Lorentz factor with the flare duration
and jet break time. In the second method, the upper limit on the Lorentz factor
is derived by assuming that the X-ray flare jet has undergone saturated
acceleration. We also re-estimate the initial Lorentz factor with GRB afterglow
onsets, and find the coefficient of the theoretical Lorentz factor is 1.67
rather than the commonly used 2 for interstellar medium (ISM) and 1.44 for the
wind case. We find that the correlation between the limited Lorentz factor and
the isotropic radiation energy of X-ray flares in the ISM case is more
consistent with that of prompt emission than the wind case in a statistical
sense. For a comparison, the lower limit on Lorentz factor is statistically
larger than the extrapolation from prompt bursts in the wind case. Our results
indicate that X-ray flares and prompt bursts are produced by the same physical
mechanism.Comment: 16 pages, 6 figures, 1 table, accepted for publication in Ap
Fast Radio Bursts from the Inspiral of Double Neutron Stars
In this paper we propose that a fast radio burst (FRB) could originate from
the magnetic interaction between double neutron stars (NSs) during their final
inspiral within the framework of a unipolar inductor model. In this model, an
electromotive force is induced on one NS to accelerate electrons to an
ultra-relativistic speed instantaneously. We show that coherent curvature
radiation from these electrons moving along magnetic field lines in the
magnetosphere of the other NS is responsible for the observed FRB signal, that
is, the characteristic emission frequency, luminosity, duration and event rate
of FRBs can be well understood. In addition, we discuss several implications of
this model, including double-peaked FRBs and possible associations of FRBs with
short-duration gamma-ray bursts and gravitational wave events.Comment: 5 pages, 2 figures, accepted for publication in ApJ Letter
Chau-Wang-Wong17 Scheme Is Experimentally More Feasible Than The Six-State Scheme
Recently, Chau et al. [Phys. Rev. A 95, 022311 (2017)] reported a
quantum-key-distribution (QKD) scheme using four-dimensional qudits.
Surprisingly, as a function of the bit error rate of the raw key, the secret
key rate of this scheme is equal to that of the (qubit-based) six-state scheme
under one-way classical communication using ideal apparatus in the limit of
arbitrarily long raw key length. Here we explain why this is the case in spite
of the fact that these two schemes are not linearly related to each other. More
importantly, we find that in terms of the four-dimensional dit error rate of
the raw key, the Chau et al.'s scheme can tolerate up to 21.6% using one-way
classical communications, which is better than the Sheridan and Scarani's
scheme [Phys. Rev. A 82, 030301(R) (2010)]. In addition, we argue the
experimental advantages of the Chau et al. implementation over the standard
six-state scheme and report a corresponding proof-of-principle experiment using
passive basis selection with decoy states. We also compare our experiment with
the recent high secret key rate implementation of the Sheridan and Scarani's
scheme by Islam et al. [Sci. Adv. \text{3}, e1701491].Comment: 8 pages, to appear in QI
PT-Symmetric magnetic Chaos in cavity magnomechanics
Here, we research a novel cavity magnomechanical system, where magnon driven
by a microwave field couples with a phonon mode with a nonlinear
magneostrictive interaction (radiation pressure-like). Based on this
interaction, we numerically demonstrate PT-symmetric chaos in this system. With
only one monochrome driving, the chaotic threshold is lowered to a rather low
levels, this is due to the dynamical enhancement of nonlinearity in the
PT-symmetry broken phase. Moreover, by simply manipulating the phase transition
between PT-symmetry phase and PT-symmetry broken phase, we can switch the
system between into and out of chaotic regimes. Our work may broaden the cavity
magnomechanics and provide a promising application for magnetic chaos-related
security communications
Characterizing high-quality high-dimensional quantum key distribution by state mapping between different degree of freedoms
Quantum key distribution (QKD) guarantees the secure communication between
legitimate parties with quantum mechanics. High-dimensional QKD (HDQKD) not
only increases the secret key rate but also tolerates higher quantum bit error
rate (QBER). Many HDQKD experiments have been realized by utilizing
orbital-angular-momentum (OAM) photons as the degree of freedom (DOF) of OAM of
the photon is a prospective resource for HD quantum information. In this work
we proposed and characterized that a high-quality HDQKD based on
polarization-OAM hybrid states can be realized by utilizing state mapping
between different DOFs. Both the preparation and measurement procedures of the
proof-of-principle verification experiment are simple and stable. Our
experiment verified that QBER and bits
secret key rate per sifted signal can be achieved for a four-dimensional QKD
with the weak coherent light source and decoy state method.Comment: 5 figures, 2 table
Measurement-Device-Independent Quantum Coin Tossing
Quantum coin tossing (QCT) is an important primitive of quantum cryptography
and has received continuous interest. However, in practical QCT, Bob's
detectors can be subjected to detector-side channel attacks launched by
dishonest Alice, which will possibly make the protocol completely insecure.
Here, we report a simple strategy of a detector-blinding attack based on a
recent experiment. To remove all the detector side channels, we present a
solution of measurement-device-independent QCT (MDI-QCT). This method is
similar to the idea of MDI quantum key distribution (QKD). MDI-QCT is loss
tolerant with single-photon sources and has the same bias as the original
loss-tolerant QCT under a coherent attack. Moreover, it provides the potential
advantage of doubling the secure distance for some special cases. Finally,
MDI-QCT can also be modified to fit the weak coherent-state sources. Thus,
based on the rapid development of practical MDI-QKD, our proposal can be
implemented easily.Comment: Close to the published versio
Unconventional phonon blockade via atom-photon-phonon interaction in hybrid optomechanical systems
Phonon nonlinearities play an important role in hybrid quantum networks and
on-chip quantum devices. We investigate the phonon statistics of a mechanical
oscillator in hybrid systems composed of an atom and one or two standard
optomechanical cavities. An efficiently enhanced atom-phonon interaction can be
derived via a tripartite atom-photon-phonon interaction, where the atom-photon
coupling depends on the mechanical displacement without practically changing a
cavity frequency. This novel mechanism of optomechanical interactions, as
predicted recently by Cotrufo et al. [Phys. Rev. Lett. 118, 133603 (2017)], is
fundamentally different from standard ones. In the enhanced atom-phonon
coupling, the strong phonon nonlinearity at a single-excitation level is
obtained in the originally weak-coupling regime, which leads to the appearance
of phonon blockade. Moreover, the optimal parameter regimes are presented both
for the cases of one- and two- cavities. We compared phonon-number correlation
functions of different orders for mechanical steady states generated in the
one-cavity hybrid system, revealing the occurrence of phonon-induced tunneling
and different types of phonon blockade. Our approach offers an alternative
method to generate and control a single phonon in the quantum regime, and has
potential applications in single-phonon quantum technologies.Comment: 11 pages,8 figures, Phys. Rev. A regular pape
Nonlinear effects in modulated quantum optomechanics
The nonlinear quantum regime is crucial for implementing interesting quantum
effects, which have wide applications in modern quantum science. Here we
propose an effective method to reach the nonlinear quantum regime in a
modulated optomechanical system (OMS), which is originally in the weak-coupling
regime. The mechanical spring constant and optomechanical interaction are
modulated periodically. This leads to the result that the resonant
optomechanical interaction can be effectively enhanced into the single-photon
strong-coupling regime by the modulation-induced mechanical parametric
amplification. Moreover, the amplified phonon noise can be suppressed
completely by introducing a squeezed vacuum reservoir, which ultimately leads
to the realization of photon blockade in a weakly coupled OMS. The reached
nonlinear quantum regime also allows us to engineer the nonclassical states
(e.g., Schr\"{o}dinger cat states) of cavity field, which are robust against
the phonon noise. This work offers an alternative approach to enhance the
quantum nonlinearity of an OMS, which should expand the applications of cavity
optomechanics in the quantum realm.Comment: 7 pages, 7 figures, Published in PR
Controlled-phase manipulation module for orbital-angular-momentum photon states
Phase manipulation is essential to quantum information processing, for which
the orbital angular momentum (OAM) of photon is a promising high-dimensional
resource. Dove prism (DP) is one of the most important element to realize the
nondestructive phase manipulation of OAM photons. DP usually changes the
polarization of light and thus increases the manipulation error for a spin-OAM
hybrid state. DP in a Sagnac interferometer also introduces a mode-dependent
global phase to the OAM mode. In this work, we implemented a high-dimensional
controlled-phase manipulation module (PMM), which can compensate the
mode-dependent global phase and thus preserve the phase in the spin-OAM hybrid
superposition state. The PMM is stable for free running and is suitable to
realize the high-dimensional controlled-phase gate for spin-OAM hybrid states.
Considering the Sagnac-based structure, the PMM is also suitable for classical
communication with spin-OAM hybrid light field.Comment: 5 pages, 6 figure
Proof-of-principle experimental realization of a qubit-like qudit-based quantum key distribution scheme
In comparison to qubit-based protocols, qudit-based quantum key distribution
(QKD) ones gen- erally allow two cooperative parties to share unconditionally
secure keys under a higher channel noise. However, it is very hard to prepare
and measure the required quantum states in qudit-based protocols in general.
One exception is the recently proposed highly error tolerant qudit-based proto-
col known as the Chau15 [1]. Remarkably, the state preparation and measurement
in this protocol can be done relatively easily since the required states are
phase encoded almost like the diagonal basis states of a qubit. Here we report
the first proof-of-principle demonstration of the Chau15 protocol. One
highlight of our experiment is that its post-processing is based on practical
one-way manner, while the original proposal in Ref. [1] relies on complicated
two-way post-processing, which is a great challenge in experiment. In addition,
by manipulating time-bin qudit and measurement with a variable delay
interferometer, our realization is extensible to qudit with high-dimensionality
and confirms the experimental feasibility of the Chau15 protocol
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