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Quantum parameter estimation in a spin-boson dephasing quantum system by periodical projective measurements 
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下载免费PDF全文 In this paper,we explore how to estimate the phase damping parameter γ and the tunneling amplitude parameter ?from a spin-boson dephasing quantum model by periodical projective measurements.The preparation of initial states is accomplished by performing the period measurements in our scheme.The parameter γ can be always estimated when projective measurement bases are chosen as θ = π/2 and φ = 0.Based on the estimated value of γ and the interval information of ?,we can select another measurement bases(θ = π/4 and φ = π/2) to obtain the estimated value of ?.A coherent control is indispensable to estimate ? if γ is in the interval of ?;whereas the control is not necessary if γ is out of the known interval of ?.We establish the relation between the optimal period time and the parameter γ or ? in terms of Fisher information.Although the optimal measurement period cannot be selected beforehand,the aforementioned relation can be utilized to adjust the measurement period to approach the optimal one. 相似文献
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We propose a decoy state quantum key distribution scheme with odd coherent state which follows sub-Poissonian distributed photon count and has low probability of the multi-photon event and vacuum event in each pulse. The numerical calculations show that our scheme can improve efficiently the key generation rate and secure communication distance. Fhrthermore, only one decoy state is necessary to approach to the perfect asymptotic limit with infinite decoy states in our scheme, but at least two decoy states are needed in other scheme. 相似文献
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By considering the identification problem of unknown but fixed Hamiltonian H = S0σ0 ＋∑i=x,y,z Siσi where σi （i = x, y, z） are pauli matrices and σ0=I, we explore the feasibility and limitation of empirically determining the Hamiltonian parameters for quantum systems under experimental conditions imposed by projective measurements and initialization procedures. It may be unsurprising to physicists that one can not obtain the knowledge of So no matter what kind of projective measurements and initialization are permitted, but the observation draws our attention to the importance of the parameter identifiability under different experimental condition. It has also been revealed that one can obtain the knowledge of ｜Sz｜ and Sx^2＋Sy^2 at most when only the projective measurement {｜0/（0｜, ｜1/（1｜} is permitted to perform on and initialize the qubit. Further more, we demonstrated that it is feasible to distinguish ｜Sx｜, ｜Sy｜, and ｜Sz｜ even without any a priori information about Hamiltonian if at least two kinds of projective measurement or initialization procedures are permitted. It should be emphasized that both projective measurements and initialization procedures play an important role in quantum system identification. 相似文献
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We present a scheme for probabilistic remote preparation of anentangled two-qubit state with three parties from a sender to eitherof two receivers. The quantum channel is composed of a partiallyentangled two-qubit state and a partially entangled three-qubitstate. We calculate the successful total probabilities of the schemein general and particular cases, respectively. We also calculatetotal classical communication cost in a general case and twoparticular cases, respectively. 相似文献
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A novel quantum memory scheme is proposed for quantum data buses in scalable quantum computers by using adjustable interaction. Our investigation focuses on a hybrid quantum system including coupled flux qubits and a nitrogen–vacancy center ensemble. In our scheme, the transmission and storage(retrieval) of quantum state are performed in two separated steps, which can be controlled by adjusting the coupling strength between the computing unit and the quantum memory. The scheme can be used not only to reduce the time of quantum state transmission, but also to increase the robustness of the system with respect to detuning caused by magnetic noises. In comparison with the previous memory scheme, about 80% of the transmission time is saved. Moreover, it is exemplified that in our scheme the fidelity could achieve 0.99 even when there exists detuning, while the one in the previous scheme is 0.75. 相似文献
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Factors influencing the signal-to-noise ratio (SNR) of lensless ghost interference with thermal incoherent light are investigated.Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object,the position of the object in the imaging system and the transverse size of the light source.Furthermore,the effects of these factors on the SNR are discussed in detail by numerical simulations. 相似文献
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This paper explores the potential of controlling quantum systems byintroducing ancillary systems and then performing unitary operationon the resulting composite systems. It generalizes the concept ofpure state controllability for quantum systems and establishes thelink between the operator controllability of the composite system andthe generalized pure state controllability of its subsystem. It isconstructively demonstrated that if a composite quantum system can betransferred between any pair of orthonormal pure vectors, then itssubsystem is generalized pure-state controllable. Furthermore, theunitary operation and the coherent control can be concretely given totransfer the system from an initial state to the target state.Therefore, these properties may be potentially applied in quantuminformation, such as manipulating multiple quantum bits and creatingentangled pure states. A concrete example has been given toillustrate that a maximally entangled pure state of a quantum systemcan be generated by introducing an ancillary system and performingopen-loop coherent control on the resulting composite system. 相似文献
