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1.
In this paper, from the original definition of fidelity in a pure state, we first give a well-defined expansion fidelity between two Gaussian mixed states. It is related to the variances of output and input states in quantum information processing. It is convenient to quantify the quantum teleportation(quantum clone) experiment since the variances of the input(output) state are measurable. Furthermore, we also give a conclusion that the fidelity of a pure input state is smaller than the fidelity of a mixed input state in the same quantum information processing. 相似文献
2.
We report methods for preparation and tomographic reconstruction of an arbitrary single-photon path qubit. The arbitrary single-photon path qubit is prepared losslessly by passing the heralded single-photon state from spontaneous parametric down-conversion through variable beam splitter. Quantum state tomography of the single-photon path qubit is implemented by introducing path-projection measurements based on the first-order single-photon quantum interference. Using the state preparation and path-projection measurements methods for the single-photon path qubit, we demonstrate preparation and complete tomographic reconstruction of the single-photon path qubit with arbitrary purity. 相似文献
3.
Quantum controlled phase gate and cluster states
generation via two superconducting quantum interference devices in a
cavity 总被引:3,自引:0,他引:3
Z.-Y. Xue G. Zhang P. Dong Y.-M. Yi Z.-L. Cao 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):333-336
A scheme for implementing 2-qubit quantum controlled phase gate (QCPG) is proposed with two superconducting quantum interference
devices (SQUIDs) in a cavity. The gate operations are
realized within the two lower flux states of the SQUIDs by using a quantized cavity field and classical microwave pulses.
Our scheme is achieved without any type of measurement, does not use the cavity mode as the data bus and only requires a very
short resonant interaction of the SQUID-cavity system. As an application of the QCPG operation, we also propose a scheme for
generating the cluster
states of many SQUIDs. 相似文献
4.
S. De Nicola R. Fedele M. A. Man'ko V. I. Man'ko 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(2):191-198
Using the tomographic probability distribution (symplectic tomogram)
describing the quantum state (instead of the wave function or
density matrix) and properties of recently introduced tomographic
entropy associated with the probability distribution, the new
uncertainty relation for the tomographic entropy is obtained.
Examples of the entropic uncertainty relation for squeezed states
and solitons of the Bose-Einstein condensate are considered. 相似文献
5.
Superpositions of squeezed states were introduced by Sanders [Phys. Rev. A 39 (1998) 4284], Schleich et al. [Phys. Rev. A 38 (1988) 1177], Xin et al. [Phys. Rev. A 50 (1994) 2865], to investigate the occurrence of nonclassical properties of the quantized radiation field. In this report we present a generalized superposition state which interpolates between two arbitrary squeezed states. Nonclassical properties of this intermediate state as function of the interpolating parameters are studied, the previous results in the literature becoming a particularization of ours. An experimental proposal to generate this state is also presented. 相似文献
6.
A new application of the W-class state is investigated for quantum state sharing (QSTS) of an arbitrary three-qubit state. We demonstrate that four sets of W-class states can be used to realize the deterministic QSTS of an arbitrary three-qubit state based on the three-qubit von Neumann measurements and the local unitary operations. Our scheme considered here is secure against certain eavesdropping attacks. 相似文献
7.
I. Raptis P. Wallden R. R. Zapatrin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):185-188
The generalization of Schmidt decomposition due to
Cartelet-Higuchi-Sudbery applied to quantum register (a system of N
qubits) is shown to acquire direct geometrical meaning: any pure
state is canonically associated with a chain of a simplicial
complex. A leading vector method is presented to calculate the
values of the coefficients of appropriate chain. 相似文献
8.
H. Prakash P. Kumar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(2):359-363
We study amplitude-squared squeezing of the Hermitian operator Zθ=Z1
cosθ+Z2 sin θ, in the most general superposition state
, of two coherent states
and
. Here operators Z1,2 are defined by
, a is annihilation operator, θ is angle, and
complex numbers C1,2 , α, β are arbitrary and only
restriction on these is the normalization condition of the state
. We define the condition for a state
to be amplitude-squared squeezed for the operator Zθ
if squeezing parameter
, where N=a+a and
. We find
maximum amplitude-squared squeezing of Zθ in the superposed
coherent state
with minimum value 0.3268 of the
parameter S for an infinite combinations with α- β= 2.16
exp [±i(π/4) + iθ/2],
and with
arbitrary values of (α+β) and θ. For this minimum
value of squeezing parameter S, the expectation value of photon number can
vary from the minimum value 1.0481 to infinity. Variations of the parameter
S with different variables at maximum amplitude-squared squeezing are also
discussed. 相似文献
9.
Entangled photon pairs must often be spatially separated for their subsequent manipulation in integrated quantum circuits. Separation that is both deterministic and universal can in principle be achieved through anti‐coalescent two‐photon quantum interference. However, such interference‐facilitated pair separation (IFPS) has not been extensively studied in the integrated setting, which has important implications on performance. This work provides a detailed review of IFPS and examines how integrated device dependencies such as dispersion impact separation fidelity and interference visibility. The analysis applies equally to both on‐chip and in‐fiber implementations. When coupler dispersion is present, the separation performance can depend on photon bandwidth, spectral entanglement and the dispersion. By design, reduction in the separation fidelity due to loss of non‐classical interference can be perfectly compensated for by classical wavelength demultiplexing effects. This work informs the design of devices for universal photon pair separation of states with tunable arbitrary properties.
10.
P. Aniello C. Lupo M. Napolitano M. G.A. Paris 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):579-587
Transformations achievable by linear optical components
allow to generate the whole unitary group only when restricted to
the one-photon subspace of a multimode Fock space. In this paper, we
address the more general problem of encoding quantum information by
multiphoton states, and elaborating it via ancillary extensions,
linear optical passive devices and photodetection. Our scheme stems
in a natural way from the mathematical structures underlying the
physics of linear optical passive devices. In particular, we analyze
an economical procedure for mapping a fiducial 2-photon 2-mode state
into an arbitrary 2-photon 2-mode state using ancillary resources
and linear optical passive N-ports assisted by post-selection. We
found that adding a single ancilla mode is enough to generate any
desired target state. The effect of imperfect photodetection in
post-selection is considered and a simple trade-off between success
probability and fidelity is derived. 相似文献
11.
A controlled quantum teleportation scheme of an N-particle unknown state via three-particle W1 states 下载免费PDF全文
In this paper a controlled quantum teleportation scheme of an N-particle unknown state is proposed when N groups of three-particle W1 states are utilized as quantum channels. The quantum information of N-particle unknown state is transmitted from the sender to the recipient under the control of all supervisors. It can be realized with a certain probability. After the sender makes Bell-state measurements and the supervisors perform the computational basis measurements, the recipient will introduce auxiliary particles and carry out unitary transformations depending on classical information from the sender and the supervisors. Finally, the computational basis measurement will be performed by the recipient to confirm whether the teleportation succeeds or not. The successful completion of the scheme relies on all supervisors' cooperation. In addition, the fidelity and security of the scheme are discussed. 相似文献
12.
H.-Y. Fan Y.-L. Yang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):107-113
For an asymmetric beam-splitter a new kind of entangled state
is introduced, we then derive the integration
measure with which such states can make up a complete and orthonormal
representation in two-mode Fock space. We then show how to use
in finding new squeezing operator and new
squeezed state, whose generation can relies on the asymmetric beamsplitter. 相似文献
13.
14.
D. PortesJr. H. Rodrigues S. B. Duarte B. Baseia 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):145-149
We study the exchange of states in coupled fields along their time
evolution. The coupling is described by a quadratic form in terms of
annihilation and creation operator in the field Hamiltonian. An analytical
approach is employed to describe the time evolution of the field state in
Fock's space and the conditions for an arbitrary initial states to be
transferred with 100% fidelity is determined. We show that only for initial
states C0|0>+CN|N>, this situation can occurs. The important
|1〉↔|0〉 qubits transfer is a particular
case of this transference of number state. The relation between the coupling
constant and characteristic field frequencies for complete state
transference is also determined. 相似文献
15.
A.-S. F. Obada G. M. Abd Al-Kader 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(1):189-198
The nonlinear extensions of the single-mode squeezed vacuum and
squeezed coherent states are studied. We have constructed the
nonlinear squeezed states (NLSS's) realization of
SU(1,1) Lie algebra. Two cases of this realization are
considered for unitary and non-unitary deformation operator
function. The nonlinear squeezed coherent states (NLSCS's)
are defined and special cases of these states are obtained.
Some nonclassical properties of these states are discussed. The
s-parameterized characteristic function and various moments are
calculated. The Glauber second-order coherence function is
calculated. The squeezing properties of the NLSCS's are studied.
Analytical and numerical results for the quadrature component
distributions for the NLSCS's are presented. A generation scheme for
NLSCS's using the trapped ions centre-of-mass motion approach is
proposed. 相似文献
16.
T. Golubeva Yu. Golubev C. Fabre N. Treps 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):179-193
In this paper, we investigate several properties of the
full signal-idler-pump mode quantum state generated by a triply
resonant non-degenerate Optical Parametric Oscillator operating
above threshold, with an injected wave on the signal and idler
modes in order to lock the phase diffusion process. We determine
and discuss the spectral purity of this state, which turns out not
to be always equal to 1 even though the three interacting modes
have been taken into account at the quantum level. We have seen
that the purity is essentially dependent on the weak
intensity of the injected light and on an asymmetry of the
synchronization. We then derive the expression of its total
three-mode Glauber P-function, and calculate the joint
signal-idler photon number probability distribution and
investigate their dependence on the injection. 相似文献
17.
Generation of Greenberger-Horne-Zeilinger states for multiple atoms trapped in separated cavities 总被引:1,自引:0,他引:1
S. B. Zheng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,54(3):719-722
We propose a scheme for generating maximally entangled states for multiple atoms trapped in distant cavities connected by
fibers. During the operation neither the atomic system nor the fibers are excited, which is important in view of decoherence.
Under certain conditions, the probability that the cavities are excited is negligible. The scheme does not include projective
measurement and the GHZ state is generated deterministically. Taking advantage of adiabatic passage, the entanglement fidelity
is insensitive to fluctuation of experimental parameters. 相似文献
18.
A. R. Usha Devi R. Prabhu M. S. Uma 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):133-138
Production and analysis of non-Gaussian radiation fields has evinced a lot of attention recently.
Simplest way of generating such non-Gaussians is through adding (subtracting) photons to
Gaussian fields.
Interestingly, when photons are added to classical Gaussian fields, the resulting states exhibit
non-classicality.
Two important classical Gaussian radiation fields are coherent and thermal states. Here, we
study the non-classical features of
such states when photons are added to them. Non-classicality of these states shows up in the
negativity of the
Wigner function. We also work out the entanglement potential, a recently proposed measure
of non-classicality for these states. Our analysis reveals that photon added coherent states are
non-classical for all seed beam intensities; their non-classicality increases with the addition
of more number of photons. Thermal state exhibits non-classicality at all temperatures, when a
photon is added; lower the temperature, higher is their non-classicality. 相似文献
19.
Phase estimation of phase shifts in two arms for an SU(1,1) interferometer with coherent and squeezed vacuum states 下载免费PDF全文
We theoretically study the quantum Fisher information(QFI) of the SU(1,1) interferometer with phase shifts in two arms by coherent ? squeezed vacuum state input, and give the comparison with the result of phase shift only in one arm.Different from the traditional Mach–Zehnder interferometer, the QFI of single-arm case for an SU(1,1) interferometer can be slightly higher or lower than that of two-arm case, which depends on the intensities of the two arms of the interferometer.For coherent ? squeezed vacuum state input with a fixed mean photon number, the optimal sensitivity is achieved with a squeezed vacuum input in one mode and the vacuum input in the other. 相似文献
20.
O. Jedrkiewicz R. Loudon J. Jeffers 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):129-140
Previous work on the retrodictive theory of direct
detection is extended to cover the homodyne detection of coherent optical
signal states
and
. The retrodictive input state probabilities are obtained by
the application of Bayes' theorem to the corresponding predictive
distributions, based on the probability operator measure (POM) elements for
the homodyne process. Results are derived for the retrodictive information
on the complex amplitude of the signal field obtainable from the difference
photocount statistics of both 4-port and 8-port balanced homodyne detection
schemes. The local oscillator is usually assumed much stronger than the
signal but the case of equal strengths in 4-port detection is also
considered. The calculated probability distributions and error rates are
illustrated numerically for values of signal and local oscillator strengths
that extend from the classical to the quantum regimes. 相似文献