量子光学态的Ridgelet变换

利用有序算符内积分技术推导出一个有用的双模算符正规乘积公式. 然后在量子力学框架下, 计算出相干态、特殊压缩相干态、中介纠缠态表象的Radon变换. 在此基础上, 通过选取“墨西哥帽”母小波函数, 分别分析了以上三种量子光学态的Ridgelet变换. 关键词： 有序算符内积分技术 Radon变换 Ridgelet变换     

Progress of quantum entanglement in a trapped-ion based quantum computer

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.     

限域量子态调控研究

电子、激子和声子等量子态在固体中的行为早已被人们所熟知. 然而,当体系的尺寸只有纳米量级的时候,已有的固体理论常常不能适用,需要新的低维物理理论的建立. 我们系统研究了低维体系限域量子态（包括电子、激子和声子）的行为对环境、应力、压力及光的响应和性质的调控. 较早认识到低维体系之显著的表面-体积比对量子态性质调控之有效性,系统地揭示了低维体系的一系列由表面和应力决定的新颖性质,证明了低维体系的表面和应力效应同量子限域效应同等重要. 本文概况了如下五个方面的结果：（1）一种使用应力效应调控电子能带结构的方法和（2）一种使用表面效应调控电子能带结构的方法（这两个方法都可将低维体系能带从间接能隙调控至直接能隙能带结构）;（3）一种低维体系表面掺杂方法,该方法将在低维体系掺杂中取代传统方法;（4）量子点表面诱导的光致异构现象;（5）基于表面自催化半导体低维结构的形成机理. 希望我们的研究工作有助于促进低维体系在光电子、纳电子、环境、能源、生物和医学等领域的应用.     

Robust quantum dot exciton generation via adiabatic passage with frequency-swept optical pulses

The energy states in semiconductor quantum dots are discrete as in atoms, and quantum states can be coherently controlled with resonant laser pulses. Long coherence times allow the observation of Rabi flopping of a single dipole transition in a solid state device, for which occupancy of the upper state depends sensitively on the dipole moment and the excitation laser power. We report on the robust population inversion in a single quantum dot using an optical technique that exploits rapid adiabatic passage from the ground to an excited state through excitation with laser pulses whose frequency is swept through the resonance. This observation in photoluminescence experiments is made possible by introducing a novel optical detection scheme for the resonant electron hole pair (exciton) generation.     

Demonstration of quantum telecloning of optical coherent states

We demonstrate unconditional telecloning for the first time. In particular, we symmetrically and unconditionally teleclone coherent states of light from one sender to two receivers, achieving a fidelity for each clone of F = 0.58 +/- 0.01, which surpasses the classical limit. This is a manipulation of a new type of multipartite entanglement whose nature is neither purely bipartite nor purely tripartite.     

Preserving quantum states using inverting pulses: a super-Zeno effect

We construct an algorithm for suppressing the transitions of a quantum mechanical system, initially prepared in a subspace P of the full Hilbert space of the system, to outside this subspace by subjecting it to a sequence of unequally spaced short-duration pulses. Each pulse multiplies the amplitude of the vectors in the subspace by -1. The number of pulses required by the algorithm to limit the leakage probability to epsilon in time increases as T exp[square root log(T(2)/epsilon)], compared to T(2)epsilon(-1) in the standard quantum Zeno effect.     

Near-field optical mapping of quantum Hall edge states

We report on the mapping of quantum-Hall edge states by quasiresonant photovoltage measurements using a near-field scanning optical microscope. We have observed fine structures near sample edges that shift inward with an increase in magnetic field in accordance with the shift of the positions of the quantum-Hall edge states. We have found a transition from the weak disorder regime where compressible-incompressble strips are visible to the strong disorder regime where fluctuations smear out incompressible strips.     

Stable rectangular pulses supported by a quantum dot optical amplifier

We predict the formation of a stable solitary rectangular pulse in semiconductor quantum dot media. The formation of such a pulse occurs when a quantum dot system is pumped in a way, where the s shell excitation exhibits gain while the p shell absorbs. We provide formulas to describe the rectangular pulse by the systems material parameters. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characteristics of wavelength conversion of short optical pulses in quantum dot semiconductor optical amplifiers

The characteristics of short optical pulse four-wave mixing (FWM) and amplification in quantum dot semiconductor optical amplifiers (QD-SOAs) are investigated taken into account the effect of the multi-discrete QD energy levels. Different saturation and recovery response for the electron and hole states are observed, which is attributed to different energy spacing between the energy states. We found that the 3 dB saturation energy of QD-SOA depends on the pulse width for short input pulses. Also, the optimum time delay between the probe and pump pulses in QD-SOAs, which provides maximum FWM efficiency in QD-SOAs, is smaller than the optimum delay in quantum well SOA.     

Fractional quantum Hall states of atoms in optical lattices

We describe a method to create fractional quantum Hall states of atoms confined in optical lattices. We show that the dynamics of the atoms in the lattice is analogous to the motion of a charged particle in a magnetic field if an oscillating quadrupole potential is applied together with a periodic modulation of the tunneling between lattice sites. In a suitable parameter regime the ground state in the lattice is of the fractional quantum Hall type, and we show how these states can be reached by melting a Mott-insulator state in a superlattice potential. Finally, we discuss techniques to observe these strongly correlated states.     

Statistical reconstruction of optical quantum states based on mutually complementary quadrature quantum measurements

We describe a new method for reconstructing the quantum state of the electromagnetic field from the results of mutually complementary optical quadrature measurements. This method is based on the root approach and displaces squeezed Fock states are used as the basis. Theoretical analysis and numerical experiments demonstrate the considerable advantage of the developed tools over those described in the literature.     

Formation of nonclassical states of vortex solitons in optical fibers with quantum dots

The problem of control for the quantum statistics of dissipative vortex optical solitons when using the Raman scheme of spin-flip transitions in an optical fiber doped with narrow-bandgap semiconductor quantum dots is considered. The possibility of forming individual bounded nonclassical quadrature squeezed light regions appearing within the spatial profile of a formed vortex soliton is demonstrated.     

Imaging with short optical pulses

A new method of three-dimensional optical imaging based on range gating with subpicosecond pulses is being developed. As opposed to other techniques of medical imaging, this new method is characterized by both high contrast and resolution. Preliminary tests demonstrate a longitudinal resolution better than 10 μm. The computer algorithm needed to reconstruct the image from the attenuated backscattering and to extend to three dimensions the one-dimensional depth resolution, is discussed.     

Statistical reconstruction of the quantum states of three-level optical systems

The procedure of measurement followed by the reconstruction of the quantum state of a three-level optical system is implemented for a frequency-and spatially degenerate two-photon field. The method of statistical estimation of the quantum state from a solution to the likelihood equation and the analysis of the statistical properties of the obtained estimators is developed. Using the root method of estimating quantum states, the initial two-photon (qutrit) wave function is reconstructed from the measured fourth-order field moments.     

Nonlinear optical properties of biexciton states in GaN quantum disks

The ground state energy of an exciton and biexciton states, in a GaN/Al_xGa_1-xN quantum disk are investigated by the variation method, within envelope function and effective mass approximations. Exciton and biexciton binding energy, and the dipole moments related to the transition between ground, exciton and biexciton states, are calculated as a function of quantum disk geometry. The optical nonlinearity via the exciton and biexciton states is studied on the basis of a three level model through the density matrix formalism. The behavior of different terms of third order susceptibility χ⁽³⁾, are studied around resonance frequencies and for different geometries of disk. The effect of values of the decay rates on χ⁽³⁾ are studied. It is found that these values have remarkable effect on the second term of, χ⁽³⁾.     

Linear optical implementation of optimal unambiguous discrimination among quantum states

In this paper, we present a linear optical scheme for optimal unambiguous discrimination among nonorthogonal quantum states in terms of the multiple-rail and polarization representation of a single photon. In our scheme, discriminated quantum states are expressed by using the spatial degree of freedom of a single photon while the polarization degree of freedom of the single photon is used to act as an auxiliary qubit. The optical components used in our scheme are only passive linear optical elements such as polarizing beam splitters, wave plates, polarizers, single photon detectors, and single photon source.     

Design and implementation of polarization filter for quantum states discriminator in optical quantum communication

In optical quantum communication, quantum state measurement is necessary. This paper proposes a new technique for realization of polarization filter based on planar lightwave circuit (PLC). This filter is used for quantum state discriminator in quantum communication and also as a Bell-state analyzer in quantum repeater. Electro-optics interferometer has been used in design and implementation of polarization filter. We use lithium niobate as a wafer material and Ti:LiNbO₃ for waveguide. Two directional couplers have been used in this device. The length and spacing of these directional couplers have been designed so that each polarization is routed in specific output. The proposed device has one input and two outputs. If polarization of the input photon is vertical, then this photon will appear in output 1, otherwise if the input photon has horizontal polarization, it appears in output 2. For vertical polarization input, the power overlaps integral (POI) shows that isolation between two outputs is 14.96 dB. As to horizontal polarization input, the isolation between two outputs is 13.8 dB. The designed polarization filter has length of 33 mm and width of 60 μm. This device is very suitable for use in integrated optics.     

Atomic coherent states and reduced quantum fluctuations in optical transients

We show that the atomic coherent states (the Bloch states) commonly encountered in coherent transient phenomena exhibit squeezing. We illustrate this property calculating the degree of squeezing and the normalized correlation coefficient g⁽²⁾ for a system of N two-level atoms interacting with a cw laser electric field.     

Localized states of flattened quantum elliptic rings and their optical properties

A flattened elliptic ring containing an electron is studied. The emphasis is placed on clarifying the effect of the flattening. The localized states are classified into four types according to their inherent nodes. When the ring becomes more flattened, the total probability of dipole absorption of each state is found to be reduced. Furthermore, each spectral line of absorption is found to shift towards red and may split into a few lines, and these lines as a whole become more diffusive.