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1.
We present a theoretical analysis of the implementation of an entangling quantum gate between two trapped Ca+ ions which is based on the dipolar interaction among ionic Rydberg states. In trapped ions, the Rydberg excitation dynamics is usually strongly affected by mechanical forces due to the strong couplings between electronic and vibrational degrees of freedom in inhomogeneous electric fields. We demonstrate that this harmful effect can be overcome using dressed states that emerge from the microwave coupling of nearby Rydberg states. At the same time. these dressed states exhibit long-range dipolar interactions which we use to implement a controlled adiabatic phase gate. Our study highlights a route toward a trapped ion quantum processor in which quantum gates are realized independently of the vibrational modes. 相似文献
2.
Generation of unconventional geometric phase gates in ion trap-optical cavity system by squeezed operators
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Based on squeezed operators this paper has implemented an ideal
unconventional geometric quantum gate (GQG) in ion trap-optical
cavity system by radiating the trapped ions with the cavity field of
frequency wc and an external laser field of frequency
wL. It can ensure that the gate time is shorter than
the coherence time for qubits and the decay time of the optical
cavity by appropriately tuning the ionic transition frequency
w0, the frequencies of the cavity mode wc and
the vibrational mode ν. It has also realized the unconventional
GQG under the influence of the cavity decay based on the
squeezed-like operators and found that the present scheme works well
for the smaller cavity decay by investigating the corresponding
fidelity and success probability. 相似文献
3.
Distributed quantum computation with superconducting qubit via LC circuit using dressed states
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A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LC circuit through mutual inductance,are used for implementing quantum gates.By using dressed states,quantum state transfer and quantum entangling gate can be implemented.With the help of the time-dependent electromagnetic field,any two dressed qubits can be selectively coupled to the data bus (the last LC circuit),then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed.As a result,the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme. 相似文献
4.
《中国物理快报》2021,(9)
Single rare-earth ions doped in solids are one kind of the promising candidates for quantum nodes towards a scalable quantum network.Realizing a universal set of high-fidelity gate operations is a central requirement for functional quantum nodes.Here we propose geometric gate operations using the hybridized states of electron spin and nuclear spin of an ion embedded in a crystal.The fidelities of these geometric gates achieve 0.98 in the realistic experimental situations.We also show the robustness of geometric gates to pulse fluctuations and to environment decoherence.These results provide insights for geometric phases in dissipative systems and show a potential application of high fidelity manipulations for future quantum internet nodes. 相似文献
5.
B. Nasr Esfahani 《International Journal of Theoretical Physics》2008,47(5):1373-1385
Fidelity for states of spin-
particles moving in a static spherically symmetric traversable wormhole spacetime is discussed. When the centroid of the corresponding
wave packet moves along a specified path in the gravitational field, both acceleration and gravity cause to transform the
state of the particle. For circular orbits of the centroid coinciding the throat of wormhole, the fidelity between initial
and final states of the whole system as well as the fidelity of the spin parts of the states are equal to the unity. This
means that, the error in quantum communication diminishes on such a paths. For fixed elapsed proper time and angular momentum
of the centroid, there always exists one circular orbit with determined radius on which the fidelity of spin parts is minimum.
The fidelity for wave packets moving along a radial geodesic toward the throat of wormhole is also discussed. In this case,
the centroid traverses the wormhole and reaches to the other side, with a perfect fidelity for the spin parts, though the
fidelity for the states of the whole system is not perfect. 相似文献
6.
In recent years, there have been significant progress toward building a practical quantum computer, demonstrating key ingredients such as single-qubit gates and a two-qubit entangling gate. Among various physical platforms for a potential quantum computing processor, a trapped-ion system has been one of the most promising platforms due to long coherence times, high-fidelity quantum gates, and qubit connectivity. However, scaling up the number of qubits for a practical quantum computing faces a core challenge in operating high-fidelity quantum gates under influence from neighboring qubits. In particular, for the trapped-ion system, unwanted quantum crosstalk between qubits and ions’ quantum motional states hinder performing high-fidelity entanglement as the number of ions increases. In this review, we introduce a trapped-ion system and explain how to perform single-qubit gates and a two-qubit entanglement. Moreover, we mainly address theoretical and experimental approaches to achieve high-fidelity and scalable entanglement toward a trapped-ion based quantum computer. 相似文献
7.
B. Nasr Esfahani M. Ahmadi F. Ahmadi 《International Journal of Theoretical Physics》2008,47(12):3130-3138
Fidelity for two-particle wave packets of spin-
particles moving around the Schwarzschild spacetime is discussed. Both acceleration and gravity cause to produce a Wigner
rotation that transforms the wave packet as it moves along a specified path in the gravitational field. For considered circular
paths, the fidelity between the spin parts of initial and final states of the system, called the spin fidelity, is obtained
as a function of angular velocity, elapsed proper time and radius of circular paths. For fixed elapsed proper time and angular
momentum of the centroid, there always exists one circular orbit with determined radius on which the fidelity of spin parts
is minimum. Using a numerical approach, the behavior of the spin fidelity in terms of the angular velocity, as well as the
radius of paths is described for both the spin singlet and spin triplet states. 相似文献
8.
M. Mahdian M. B. Jeddi M. Yahyavi M. Marahem 《International Journal of Theoretical Physics》2013,52(11):3830-3843
We consider the dynamics of quantum correlations of two coupled spin qubits with Dzyaloshinsky-Moriya (DM) interaction influenced by a local external magnetic field along the z-direction and coupled to bath spin- $\frac{1}{2}$ particles as independent non-Markovian environment. For this model, we calculate the entanglement measure of concurrence, quantum discord and quantum dissonance and find effects of DM interaction, bath-system coupling constant and temperature on the dynamics of quantum correlation. At last, we obtain the teleportation for this model by using fidelity and observe changes of DM interaction, bath-system coupling constant, temperature and magnetic field on fidelity. 相似文献
9.
The quantum Hall effect is usually observed when a two-dimensional electron gas is subjected to an external magnetic field, so that their quantum states form Landau levels. In this work we predict that a new phenomenon, the quantum anomalous Hall effect, can be realized in Hg{1-y}Mn{y}Te quantum wells, without an external magnetic field and the associated Landau levels. This effect arises purely from the spin polarization of the Mn atoms, and the quantized Hall conductance is predicted for a range of quantum well thickness and the concentration of the Mn atoms. This effect enables dissipationless charge current in spintronics devices. 相似文献
10.
O'Brien JL Pryde GJ Gilchrist A James DF Langford NK Ralph TC White AG 《Physical review letters》2004,93(8):080502
We demonstrate complete characterization of a two-qubit entangling process--a linear optics controlled-NOT gate operating with coincident detection--by quantum process tomography. We use a maximum-likelihood estimation to convert the experimental data into a physical process matrix. The process matrix allows an accurate prediction of the operation of the gate for arbitrary input states and a calculation of gate performance measures such as the average gate fidelity, average purity, and entangling capability of our gate, which are 0.90, 0.83, and 0.73, respectively. 相似文献
11.
12.
Chen J Altepeter JB Medic M Lee KF Gokden B Hadfield RH Nam SW Kumar P 《Physical review letters》2008,100(13):133603
We present the first quantum controlled-not (cnot) gate realized using a fiber-based indistinguishable photon-pair source in the 1.55 microm telecommunications band. Using this free-space cnot gate, all four Bell states are produced and fully characterized by performing quantum-state tomography, demonstrating the gate's unambiguous entangling capability and high fidelity. Telecom-band operation makes this cnot gate particularly suitable for quantum-information-processing tasks that are at the interface of quantum communication and linear optical quantum computing. 相似文献
13.
As a special quantum node in a quantum network, the quantum router plays an important role in storing and transferring quantum information. In this paper, we propose a quantum router scheme based on asymmetric intercavity couplings and a three-level Λ-type atomic system. This scheme implements the quantum routing capability very well. It can perfectly transfer quantum information from one quantum channel to another. Compared with the previous quantum routing scheme, our proposed scheme can achieve the transfer rate of single photons from one quantum channel to another quantum channel reaching 100%, the high transfer rate is located in the almost quadrant regions with negative values of the two variables λ_a and λ_b, and their maximum values T_u~b+T_d~b= 1 emerge in the center point λ_a=λ_b=-1. Therefore, it is possibly feasible to efficiently enhance the routing capability of the single photons between two channels by adjusting the inter-resonator couplings, and the asymmetric intercavity coupling provides a new method for achieving high-fidelity quantum routers. 相似文献
14.
We investigate the quantum numbers of the pentaquark states ${{\rm{P}}}_{{\rm{c}}}^{+}$, which are composed of 4 (three flavors) quarks and an antiquark, by analyzing their inherent nodal structure in this paper. Assuming that the four quarks form a tetrahedron or a square, and the antiquark is at the ground state, we determine the nodeless structure of the states with orbital angular moment L≤3, and in turn, the accessible low-lying states. Since the inherent nodal structure depends only on the inherent geometric symmetry, we propose the quantum numbers JP of the low-lying pentaquark states ${{\rm{P}}}_{c}^{+}$ may be ${\tfrac{3}{2}}^{-}$, ${\tfrac{5}{2}}^{-}$, ${\tfrac{3}{2}}^{+}$and ${\tfrac{5}{2}}^{+}$, independent of dynamical models. 相似文献
15.
P. Kok 《Optics and Spectroscopy》2011,111(4):520-522
Optical NOON states ${{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} \mathord{\left/
{\vphantom {{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} {\sqrt 2 }}} \right.
\kern-\nulldelimiterspace} {\sqrt 2 }}${{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} \mathord{\left/
{\vphantom {{\left( {\left| {\left. {N,0} \right\rangle + } \right|\left. {0,N} \right\rangle } \right)} {\sqrt 2 }}} \right.
\kern-\nulldelimiterspace} {\sqrt 2 }} are an important resource for Heisenberg-limited metrology and quantum lithography. The only known methods for creating NOON
states with arbitrary N via linear optics and projective measurements seem to have a limited range of application due to imperfect phase control.
Here, we show that bootstrapping techniques can be used to create high-fidelity NOON states of arbitrary size. 相似文献
16.
H. Mohammadi S. J. Akhtarshenas F. Kheirandish 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,62(3):439-447
We study the entanglement dynamics of an anisotropic two-qubit Heisenberg XYZ system in
the presence of intrinsic decoherence. The usefulness of such a system for performance of
the quantum teleportation protocol T0\mathcal{T}_0
and entanglement teleportation protocol T1\mathcal{T}_1
is also investigated. The results depend on the initial conditions and the parameters of
the system. The roles of system parameters such as the inhomogeneity of the magnetic field
b and the spin-orbit interaction parameter D, in
entanglement dynamics and fidelity of teleportation, are studied for both product and
maximally entangled initial states of the resource. We show that for the product and
maximally entangled initial states, increasing D amplifies the effects of
dephasing and hence decreases the asymptotic entanglement and fidelity of the
teleportation. For a product initial state and specific interval of the magnetic field
B, the asymptotic entanglement and hence the fidelity of teleportation
can be improved by increasing B. The XY and XYZ Heisenberg systems
provide a minimal resource entanglement, required for realizing efficient teleportation.
Also, in the absence of the magnetic field, the degree of entanglement is preserved for
the maximally entangled initial states $\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {00} \right\rangle \pm } \right|\left. {11} \right\rangle } \right)} \right.. The
same is true for the maximally entangled initial states
$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right.$\left| {\psi \left. {\left( 0 \right)} \right\rangle = \frac{1}
{{\sqrt 2 }}\left( {\left| {\left. {01} \right\rangle \pm } \right|\left. {10} \right\rangle } \right)} \right., in the
absence of spin-orbit interaction D and the inhomogeneity parameter
b. Therefore, it is possible to perform quantum teleportation protocol
T0\mathcal{T}_0
and entanglement teleportation T1\mathcal{T}_1,
with perfect quality, by choosing a proper set of parameters and employing one of these
maximally entangled robust states as the initial state of the resource. 相似文献
17.
B. Nasr Esfahani F. Ahmadi M. Ahmadi 《International Journal of Theoretical Physics》2009,48(7):1957-1964
Fidelity for the spin part of states of two spin-
particles is investigated from the viewpoint of moving observers. Using a numerical approach, the behavior of the fidelity
in terms of the boost parameter is described for different amounts of spin entanglement and momentum entanglement. It is shown
that for the spin entangled states the fidelity decreases less than that of the case of spin product states and there are
special cases for which the fidelity remains perfect regardless of moving observers’ velocity. Generally, in the limit of
boosts with speeds close to the speed of light, the fidelity saturates, i.e., it reaches to a constant value that depends
on the amount of momentum entanglement and the width of the momentum distribution function. 相似文献
18.
By utilizing single particle interferometry, the fidelity or coherence of a pair of quantum states is identified with their capacity for interference. We consider processes acting on the internal degree of freedom (e.g., spin or polarization) of the interfering particle, preparing it in states rho_{A} or rho_{B} in the respective path of the interferometer. The maximal visibility depends on the choice of interferometer, as well as the locality or nonlocality of the preparations, but otherwise depends only on the states rho_{A} and rho_{B} and not the individual preparation processes themselves. This allows us to define interferometric measures which probe locality and correlation properties of spatially or temporally separated processes, and can be used to differentiate between processes that cannot be distinguished by direct process tomography using only the internal state of the particle. 相似文献
19.
Dynamical quantum phase transition in XY chains with the Dzyaloshinskii-Moriya and XZY-YZX three-site interactions
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Kaiyuan Cao 《中国物理 B》2022,31(6):60505-060505
We study the dynamical quantum phase transitions (DQPTs) in the $XY$ chains with the Dzyaloshinskii-Moriya interaction and the $XZY$-$YZX$ type of three-site interaction after a sudden quench. Both the models can be mapped to the spinless free fermion models by the Jordan-Wigner and Bogoliubov transformations with the form $H=\sum_{k}ǎrepsilon_{k}(\eta^{†}_{k}\eta_{k}-\frac{1}{2})$, where the quasiparticle excitation spectra $ǎrepsilon_{k}$ may be smaller than 0 for some $k$ and are asymmetrical ($ǎrepsilon_{k}\neqǎrepsilon_{-k}$). It is found that the factors of Loschmidt echo equal 1 for some $k$ corresponding to the quasiparticle excitation spectra of the pre-quench Hamiltonian satisfying $ǎrepsilon_{k}\cdotǎrepsilon_{-k}<0$, when the quench is from the gapless phase. By considering the quench from different ground states, we obtain the conditions for the occurrence of DQPTs for the general $XY$ chains with gapless phase, and find that the DQPTs may not occur in the quench across the quantum phase transitions regardless of whether the quench is from the gapless phase to gapped phase or from the gapped phase to gapless phase. This is different from the DQPTs in the case of quench from the gapped phase to gapped phase, in which the DQPTs will always appear. Moreover, we analyze the different reasons for the absence of DQPTs in the quench from the gapless phase and the gapped phase. The conclusion can also be extended to the general quantum spin chains. 相似文献
20.
We investigate experiments of continuous-variable quantum information processing based on the teleportation scheme. Quantum
teleportation, which is realized by a two-mode squeezed vacuum state and measurement-and-feedforward, is considered as an
elementary quantum circuit as well as quantum communication. By modifying ancilla states or measurement-and-feedforwards,
we can realize various quantum circuits which suffice for universal quantum computation. In order to realize the teleportation-based
computation we improve the level of squeezing, and fidelity of teleportation. With a high-fidelity teleporter we demonstrate
some advanced teleportation experiments, i.e., teleportation of a squeezed state and sequential teleportation of a coherent
state. Moreover, as an example of the teleportation-based computation, we build a QND interaction gate which is a continuous-variable
analog of a CNOT gate. A QND interaction gate is constructed only with ancillary squeezed vacuum states and measurement-and-feedforwards.
We also create continuous-variable four mode cluster type entanglement for further application, namely, one-way quantum computation. 相似文献