14,960 research outputs found
Error-rejecting quantum computing with solid-state spins assisted by low-Q optical microcavities
We present an efficient proposal for error-rejecting quantum computing with
quantum dots (QD) embedded in single-sided optical microcavities based on the
interface between the circularly polarized photon and QDs. An almost unity
fidelity of the quantum entangling gate (EG) can be implemented with a
detectable error that leads to a recycling EG procedure, which improves further
the efficiency of our proposal along with the robustness to the errors involved
in imperfect input-output processes. Meanwhile, we discuss the performance of
our proposal for the EG on two solid-state spins with currently achieved
experiment parameters, showing that it is feasible with current experimental
technology. It provides a promising building block for solid-state quantum
computing and quantum networks.Comment: 8 pages, 3 figure
Heralded high-efficiency quantum repeater with atomic ensembles assisted by faithful single-photon transmission
Quantum repeater is one of the important building blocks for long distance
quantum communication network. The previous quantum repeaters based on atomic
ensembles and linear optical elements can only be performed with a maximal
success probability of 1/2 during the entanglement creation and entanglement
swapping procedures. Meanwhile, the polarization noise during the entanglement
distribution process is harmful to the entangled channel created. Here we
introduce a general interface between a polarized photon and an atomic ensemble
trapped in a single-sided optical cavity, and with which we propose a
high-efficiency quantum repeater protocol in which the robust entanglement
distribution is accomplished by the stable spatial-temporal entanglement and it
can in principle create the deterministic entanglement between neighboring
atomic ensembles in a heralded way as a result of cavity quantum
electrodynamics. Meanwhile, the simplified parity check gate makes the
entanglement swapping be completed with unity efficiency, other than 1/2 with
linear optics. We detail the performance of our protocol with current
experimental parameters and show its robustness to the imperfections, i.e.,
detuning and coupling variation, involved in the reflection process. These good
features make it a useful building block in long distance quantum
communication.Comment: 11 pages, 10 figure
Selective-Resonance-Based Quantum Entangling Operation on Qubits in Circuit QED
We present a fast quantum entangling operation on superconducting qubits
assisted by a resonator in the quasi-dispersive regime with a new effect ---
the selective resonance coming from the amplified qubit-state-dependent
resonator transition frequency and the tunable period relation between a wanted
quantum Rabi oscillation and an unwanted one. This operation does not require
any kind of drive fields and the interaction between qubits. More interesting,
the non-computational third excitation states of the charge qubits can play an
important role in shortening largely the operation time of the entangling
gates. All those features provide an effective way to realize much faster
quantum entangling gates on superconducting qubits than previous proposals.Comment: 5 pages, 4 figure
Universal quantum gates on electron-spin qubits with quantum dots inside single-side optical microcavities
We present some compact quantum circuits for a deterministic quantum
computing on electron-spin qubits assisted by quantum dots inside single-side
optical microcavities, including the CNOT, Toffoli, and Fredkin gates. They are
constructed by exploiting the giant optical Faraday rotation induced by a
single-electron spin in a quantum dot inside a single-side optical microcavity
as a result of cavity quantum electrodynamics. Our universal quantum gates have
some advantages. First, all the gates are accomplished with a success
probability of 100% in principle. Second, our schemes require no additional
electron-spin qubits and they are achieved by some input-output processes of a
single photon. Third, our circuits for these gates are simple and economic.
Moreover, our devices for these gates work in both the weak coupling and the
strong coupling regimes, and they are feasible in experiment.Comment: 13 pages, 6 figures, a single column. The negligible error on the
schematic figures for some PBSs in Opt. Express 22, 593-607 (2014) is
correcte
Secure Direct Communication with a Quantum One-Time-Pad
Quantum secure direct communication is the direct communication of secret
messages without first producing a shared secret key. It maybe used in some
urgent circumstances. Here we propose a quantum secure direct communication
protocol using single photons. The protocol uses batches of single photons
prepared randomly in one of four different states. These single photons serve
as a one-time-pad which are used directly to encode the secret messages in one
communication process. We also show that it is unconditionally secure. The
protocol is feasible with present-day technique.Comment: 4 pages and one figur
Scalable quantum computing based on stationary spin qubits in coupled quantum dots inside double-sided optical microcavities
Quantum logic gates are the key elements in quantum computing. Here we
investigate the possibility of achieving a scalable and compact quantum
computing based on stationary electron-spin qubits, by using the giant optical
circular birefringence induced by quantum-dot spins in double-sided optical
microcavities as a result of cavity quantum electrodynamics. We design the
compact quantum circuits for implementing universal and deterministic quantum
gates for electron-spin systems, including the two-qubit CNOT gate and the
three-qubit Toffoli gate. They are compact and economic, and they do not
require additional electron-spin qubits. Moreover, our devices have good
scalability and are attractive as they both are based on solid-state quantum
systems and the qubits are stationary. They are feasible with the current
experimental technology, and both high fidelity and high efficiency can be
achieved when the ratio of the side leakage to the cavity decay is low.Comment: 12 pages, 5 figures, one colum
Bulge formation in very late-type galaxies
The dynamical evolution of super star clusters (SSCs) moving in the
background of a dark matter halo has been investigated as a possible event
responsible for the formation of bulges in late-type spirals. The underlying
physical processes include sinking of SSCs due to the dynamical friction and
stripping of SSCs on their way to the center. Based on the assumption of a
universal density profile for the dark matter halo, and an isothermal model for
the SSCs, our simulations have yielded bulges that are similar in many aspects
to the observational ones. In particular, the derived surface density profiles
can be well fitted by an exponential structure with nuclear cusps, which is
consistent with HST observations.The preliminary simulations with the Burkert
density profile yield very instructive predictions on the bulge formation,
which is surely worth further investigating.Comment: 5 pages, 2 figures, style file included, 5th Sino-Germany Workshop on
Cosmology and Galaxy Formatio
Residual effect on the robustness of multiqubit entanglement
We investigate the relation between the entanglement and the robustness of a
multipartite system to a depolarization noise. We find that the robustness of a
two-qubit system in an arbitrary pure state depends completely on its
entanglement. However, this is not always true in a three-qubit system. There
is a residual effect on the robustness of a three-qubit system in an arbitrary
superposition of Greenberger-Horne-Zeilinger state and W state. Its
entanglement determines the trend of its robustness. However, there is a
splitting on its robustness under the same entanglement. Its robustness not
only has the same periodicity as its three-tangle but also alters with its
three-tangle synchronously. There is also a splitting on the robustness of an
-qubit () system although it is more complicated.Comment: 5 pages, 4 figures; A figure is added, compared with the version
published in Phys. Rev. A 82, 014301 (2010
Efficient quantum entanglement distribution over an arbitrary collective-noise channel
We present an efficient quantum entanglement distribution over an arbitrary
collective-noise channel. The basic idea in the present scheme is that two
parties in quantum communication first transmit the entangled states in the
frequency degree of freedom which suffers little from the noise in an optical
fiber. After the two parties share the photon pairs, they add some operations
and equipments to transfer the frequency entanglement of pairs into the
polarization entanglement with the success probability of 100\%. Finally, they
can get maximally entangled polarization states with polarization independent
wavelength division multiplexers and quantum frequency up-conversion which can
erase distinguishability for frequency. Compared with conventional entanglement
purification protocols, the present scheme works in a deterministic way in
principle. Surprisingly, the collective noise leads to an additional advantage.Comment: 6 pages, 2 figure
Hyper-parallel photonic quantum computation with coupled quantum dots
It is well known that a parallel quantum computer is more powerful than a
classical one. So far, there are some important works about the construction of
universal quantum logic gates, the key elements in quantum computation.
However, they are focused on operating on one degree of freedom (DOF) of
quantum systems. Here, we investigate the possibility of achieving scalable
hyper-parallel quantum computation based on two DOFs of photon systems. We
construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating on
both the spatial-mode and the polarization DOFs of a two-photon system
simultaneously, by exploiting the giant optical circular birefringence induced
by quantum-dot spins in double-sided optical microcavities as a result of
cavity quantum electrodynamics (QED). This hyper-CNOT gate is implemented by
manipulating the four qubits in the two DOFs of a two-photon system without
auxiliary spatial modes or polarization modes. It reduces the operation time
and the resources consumed in quantum information processing, and it is more
robust against the photonic dissipation noise, compared with the integration of
several cascaded CNOT gates in one DOF.Comment: 11 pages, 4 figures, one colum
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