Partial standard quantum process tomography
With the general theorem of SQPT, we shall develop a scheme to detemine an arbitrary matrix element of $chi$, which is expanded with the Choi operators, in a scalbe way.
quant-ph↗
arXiv subjects
Xiaohua Wu
Publications and source records attributed to Xiaohua Wu.
Economical standard quantum process tomography
Recently, Bendersky \emph{et al.} developed a method to complete the task of characterizing an arbitrary $χ$ matrix element in a scalable way, Phys. Rev. Lett. Vol. \textbf{100}, 190403(2008), where an auxiliary system was needed. In present work, we shall show that the same task can also be completed within the scheme of standard quantum process tomography (SQPT) where there is no requirement for ancilla. Our method depends on two observations: With the elaborately chosen operators basis, the SQPT may have an economical form where a single run of experiment, in which we measure the expectation value of a chosen operator in the outport of the quantum channel with a known input, is sufficient to characterize a selected $χ$ matrix element; With the progress recently achieved in quantum entanglement detection, we also find that the number of the experimental settings to realize the experiment for the selected $χ$ matrix element does not exceed 2N for the N-qubits system. For practice, our scheme can be applied for the cases where the controlled two-body interaction is neither available nor desirable.
quant-ph↗
Designing optimal quantum cloning machine for qubit system
Following the work of Niu and Griffiths, in \emph{Phys.Rev.A 58, 4377(1998)}, we shall investigate the problem, how to design the optimal quantum cloning machines (QCMs) for qubit system, with the help of Bloch-sphere representation. In stead of the quality factor there, the Fiuráusek's optimal condition, where the optimal cloning machine should maximize a convex mixture of the average fidelity, is used as the optimality criterion in present protocol. Almost all of the known optimal QCMs in previous works, the cloning for states with fixed polar angle, the phase-covariant cloning, the universal QCMs, the cloning for two arbitrary pure states, and the mirror phase-covariant cloning, should be discussed in a systematic way. The known results, the optimal fidelities for various input ensembles according to different optimality criteria, are recovered here. Our present scheme also offers a general way of constructing the unitary transformation to realize the optimal cloning.
quant-ph↗
Five-Fold Reduction of Lasing Threshold near the First $ΓL$-Pseudogap of ZnO Inverse Opals
We report room temperature lasing in ZnO inverse opal photonic crystals in the near-ultraviolet (UV) frequency. We observe random lasing due to disorder in the structures when the photonic pseudogaps are located away from the ZnO gain spectrum. Tuning the first $ΓL$-pseudogap to the gain peak leads to a five-fold reduction in lasing threshold and frequency shift of lasing modes due to the enhanced confinement of light.
physics.optics↗
Designing the unambiguous discriminator from the one -photon interferometer
In this paper, we shall show that the question of quanum state unambiguous discrimination can be solved by reducing it to the known problem of quantum states filtering.
quant-ph↗
Statistical studies of random lasing modes and amplified spontaneous emission spikes in weakly scattering systems
We measured the ensemble-averaged spectral correlation functions and statistical distributions of spectral spacing and intensity for lasing modes in weakly scattering systems, and compared them to those of the amplified spontaneous emission spikes. Their dramatic differences illustrated the distinct physical mechanisms. Our numerical simulation revealed that even without reabsorption the number of potential lasing modes might be greatly reduced by local excitation of a weakly scattering system. The lasing modes could be drastically different from the quasimodes of the passive system due to selective amplification of the feedback from the scatterers within the local gain region.
physics.optics↗
A New Approach to the Calculation of Some Properties of Vacuum and $π$ and $σ$ Mesons
It is shown in a systematic way that the instanton dilute model can be combined with the global colour symmetry model to form a new nonperturbative QCD model. Based on the quark propagator derived in the instanton dilute liquid approximation, the quark condensate $<\bar{q}q>$, the mixed quark gluon condensate $g_{s}<\bar{q}G_{μν}σ^{μν}q>$, the four quark condensate $<|bar{q}Γq\bar{q}Γq>$ and tensor, pion vacuum susceptibilities have been calculated at the mean field level in the framework of the new nonperturbative QCD model. The numerical results are compatible with the values obtained within other nonperturbative approaches. The calculated masses and decay constants of $π$ and $σ$ mesons are also close to the experimental values.
hep-ph↗