共查询到20条相似文献,搜索用时 15 毫秒
1.
We analyze the dynamics of a continuously observed, damped, microwave-driven solid state charge qubit, consisting of a single electron in a double well potential. The microwave field induces transitions between the qubit eigenstates, which have a profound effect on the detector output current. Useful information about the qubit dynamics, such as dephasing and relaxation rates, and the Rabi frequency, can be extracted from the detector conductance and output noise power spectrum. We also propose a technique for single-shot electron spin readout, for spin based quantum information processing, which has a number of practical advantages over existing schemes. 相似文献
2.
Hideaki Takayanagi Hirotaka Tanaka Shiro Saito Hayato Nakano 《Superlattices and Microstructures》2002,32(4-6)
The states of a flux qubit with three Josephson junctions were observed with a dc-SQUID. The qubit is an aluminium superconductor loop surrounded by a dc-SQUID for readout. It has two states, which have persistent currents flowing in opposite directions. The system potentially offers the advantage of allowing single-shot/single-system measurements of macroscopic superposition of the two states. We have developed a highly sensitive, low-noise, single-shot detection system, and here we report the first direct observation of a macroscopic quantum superposition. The measured ground and the first excited state showed the same behaviour as the theoretical ones. We also showed that the measured behaviour of the switching current in a dc-SQUID was the same as that of the quantum-mechanically expected value of the switching current in the qubit. 相似文献
3.
João Batista Rosa Silva 《Optics Communications》2008,281(9):2705-2709
This work describes how to implement probabilistically the entangled state (∣0 0 0〉 + ∣0 1 1〉 + ∣1 0 1〉 + ∣1 1 0〉)/2, for coherent state qubit, using only linear optics and measurements. Its creation is proposed firstly using an ideal lossless setup and secondly considering the decoherence caused by losses in the optical devices. The advantage of our scheme is the absence of single-qubit gates, photons counters and quantum teleportation, resources that are common in coherent state quantum information processing. 相似文献
4.
5.
J. L. Guo H. S. Song 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(2):265-269
We study the thermal entanglement in the two-qubit Heisenberg XXZ model with the Dzyaloshinskii-Moriya (DM) interaction, and teleport an unknown state using the model in thermal equilibrium state as a quantum channel. The effects of DM interaction, including Dx and Dz interaction, the anisotropy and temperature on the entanglement and fully entangled fraction are considered. What deserves mentioning here is that for the antiferromagnetic case, the Dx interaction can be more helpful for increasing the entanglement and critical temperature than Dz, but this cannot for teleportation. 相似文献
6.
Based on single Cesium atoims trapped in a 1064 nm microscopic optical trap we have exhibited a single qubit encoded in the Cesium "clock states". The single qubit initialization, detection and the fast state rotation with high efficiencies are demonstrated and this state manipulation is crucial for quantmn information processing. The ground ~ates Rabi flopping rate of 229.0 ± 0.6 kHz is realized hy a two-photon Raman process. A clock states dephasing time of 3.0 ± 0.7 ms is measured, while all irreversible homogeneous dephasing time of 124 ± 17 ms is achieved by using the spin-echo technique. This well-controlled single atom provides an ideal quantmn qubit and quantmn node for quantum information processing. 相似文献
7.
《Physics letters. A》2006,359(2):103-109
We discuss a state discriminator that unambiguously distinguishes between two quantum registers prepared with multiple copies of two unknown qubits. This device achieves the optimal performance by von Neumann measurement and general POVM in different ranges of the input preparation probabilities, respectively, and in the limit of very large program registers the optimal measurement reduces to only von Neumann measurements. 相似文献
8.
We study a readout scheme of a superconducting flux qubit state with a Cooper pair box as a transmon. The qubit states consist of the superpositions of two degenerate states where the charge and phase degrees of freedom are entangled. Owing to the robustness of the transmon against external fluctuations, our readout scheme enables the quantum non-demolition and single-shot measurement of flux qubit states. The qubit state readout can be performed by using the nonlinear Josephson amplifiers after a π/2 rotation driven by an ac electric field. 相似文献
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10.
We show a scheme to distribute the entanglement by using three-mode separable Gaussian state prepared with imperfect equipments.The scheme achieves the aim that the entanglement is distributed between two distant parties with only Gaussian operations and linear optics elements.Moreover,we analyse the logarithmic negativity of the entanglement shared between the two parties when the systems are imperfect and arrive at the conclusion that the logarithmic negativity is asymptotically stable with fluctuations within a certain space range. 相似文献
11.
We present the optimal scheme for estimating a pure qubit state by means of local measurements on N identical copies. We give explicit examples for low N. For large N, we show that the fidelity saturates the collective measurement bound up to order 1/N. When the signal state lays on a meridian of the Bloch sphere, we show that this can be achieved without classical communication. 相似文献
12.
Noisy teleportation of qubit states via the Greenberger-Horne-Zeilinger state or the W state 下载免费PDF全文
The effects of distributing entanglement through the amplitude
damping channel or the phase damping channel on the teleportation of
a single-qubit state via the Greenberger--Horne--Zeilinger state and the W
state are discussed. It is found that the average fidelity of
teleportation depends on the type and rate of the damping in the
channel. For the one-qubit affected case, the
Greenberger--Horne--Zeilinger state is as robust as the W state,
i.e., the same quantum information is preserved through
teleportation. For the two-qubit affected case, the W state is more robust
when the entanglement is distributed via the amplitude damping
channel; if the entanglement is distributed via the phase damping
channel, the W state is more robust when the noisy parameter is
small while the Greenberger--Horne--Zeilinger state becomes more
robust when it is large. For the three-qubit affected case, the
Greenberger--Horne--Zeilinger state is more robust than the W
state. 相似文献
13.
Preparation of optimal entropy squeezing state of atomic qubit inside the cavity via two-photon process and manipulation of atomic qubit outside the cavity 下载免费PDF全文
Considering two atomic qubits initially in Bell states, we send one qubit into a vacuum cavity with two-photon resonance and leave the other one outside. Using quantum information entropy squeezing theory, the time evolutions of the entropy squeezing factor of the atomic qubit inside the cavity are discussed for two cases, i.e., before and after rotation and measurement of the atomic qubit outside the cavity. It is shown that the atomic qubit inside the cavity has no entropy squeezing phenomenon and is always in a decoherent state before the operating atomic qubit outside the cavity. However,the periodical entropy squeezing phenomenon emerges and the optimal entropy squeezing state can be prepared for the atomic qubit inside the cavity by adjusting the rotation angle, choosing the interaction time between the atomic qubit and the cavity, controlling the probability amplitudes of subsystem states. Its physical essence is cutting the entanglement between the atomic qubit and its environment, causing the atomic qubit inside the cavity to change from the initial decoherent state into maximum coherent superposition state, which is a possible way of recovering the coherence of a single atomic qubit in the noise environment. 相似文献
14.
A system of two initially entangled qubits interacting with a bosonic environment is considered. The interaction induces a loss of the initial entanglement of the two qubits, and for specific initial states it causes entanglement sudden death. An investigation of the modifications on the entanglement dynamics by a single pulse control field, performed in the two qubit system, shows that the control field can not only protect entangled states against sudden death but also induce a revival of entanglement in the two qubit system. 相似文献
15.
Scheme for teleportation of unknown single qubit state via continuous variables entangling channel 下载免费PDF全文
A new scheme for quantum teleportation of single quantum bit state with using continuous variables entangling channel is presented.In our scheme two entangled light fields are employed.An outstanding characteristic of this scheme is that one atomic state is transmitted directly to another atom without using the third atom as the mediate. 相似文献
16.
利用Quantum Discord(QD)判据,研究了与热库相互作用的二比特体系的量子关联性质.讨论了在不同初态下体系量子关联随时间的变化,以及热库的平均光子数m,n和原子的自发辐射率γ对体系量子关联性质的影响.结果表明,在不同的初态下,体系可以得到不同性质的量子关联;而且当原子自发辐射率γ取固定值时,QD的衰减会随m,n取值的减小而减慢,热库平均光子数都为零的情况下能够得到最大范围的量子关联;此外,当热库平均光子数m,n取确定值时,随着γ取值的减小,QD的衰减也会随之减慢,此时同样会得到较大范围的量子关联.说明较小的热库平均光子数以及原子自发辐射率γ能够减弱QD的衰减,从而获得生命力较强的体系量子关联. 相似文献
17.
Michael Siomau 《Physics letters. A》2011,375(38):3340-3342
Suppose, we are given two finite ensembles of pure qubit states, so that the qubits in each ensemble are prepared in identical (but unknown for us) states lying on the equator of the Bloch sphere. What is the best strategy to estimate fidelity between these two finite ensembles of qubit states? We discuss three possible strategies for the fidelity estimation. We show that the best strategy includes two stages: a specific unitary transformation on two ensembles and state estimation of the output states of this transformation. 相似文献
18.
Gui-Long GaoLiusheng Xi Guoliang GaoJianping Zhong Nian-Quan Jiang 《Physics letters. A》2011,375(45):3946-3949
We design a pure solid-device comprised by LC circuits, which are coupled to superconducting charge qubit to entangle superconducting LC coherent modes. The operation time of the state of the system does not increase with the increase of the number of LC modes. Based on the measurement of charge states, an arbitrary mode of the state can be easily generated. A brief discussion about the experimental feasibility of the scheme is also shown. 相似文献
19.
This paper realizes a nondestructive and complete Bell-state analysis for atomic qubit systems by a designed nondestructive and complete Bell-state analyser. In the scheme, Bell states are completely discriminated by two bits of classical informations which comes from the locality single atom detection on two auxiliary atoms, during which the Bell states are not affected. The needed devices are well within the bounds of current technology, and then the scheme is experimentally feasible. 相似文献
20.
We give a new non-singular spherically symmetric and separable copy of the vacuum in Landau gauge for SU(2) Yang-Mills theories. The solution can be considered as a generalization of Gribov's solution in Coulomb gauge and thus it demonstrates the similarity between vacua in Coulomb and Landau gauges. 相似文献