Coherent Input Research Articles

Scalable quantum computation via a coherent state input–output process in a low-Q cavity in the atom–cavity intermediate coupling region

We propose a basic scheme to construct a hybrid controlled phase-flip (CPF) gate between a flying pulse qubit and a stationary atomic qubit, assisted by a cavity input–output process for a low-Q cavity in the atom–cavity intermediate coupling region. The qubits can be encoded on the coherent states and ground states of the single-trapped L-level atom, respectively. We present a theoretical model of the hybrid CPF gate, whose basic strategy is to control the reflectivity of the input coherent optical pulse to obtain a phase shift conditioned by the different internal atomic states by adjusting the parameters of the cavity quantum electrodynamics (CQED) system. The resulting basic scheme can be used to construct nonlocal gates between remote atomic qubits confined in spatially separated cavities, and also for the generation of an atomic cluster state. The performance and experimental feasibilities of the proposed scheme indicate that it is robust against practical noise and feasible with current technologies. Thus, our scheme is applicable for use in large-scale quantum computation.

Seismic soil-structure interaction with consideration of spatial incoherence of seismic ground motions: A case study

This paper presents a case study of seismic soil-structure interaction (SSI) analysis with consideration of spatial incoherence of seismic input ground motions. The SSI analyses were performed using the SASSI computer program for the Auxiliary Control Building (ACB) structure of an existing nuclear power plant on a hard rock site located in the Center and Eastern United States (CEUS) region. The incoherent seismic input motions for the hard rock site used for the analyses were generated using the computer program INCOH that works together with SASSI. The objective of the analyses was to generate maximum seismic response parameters for assessment of potential impact of newly developed site-specific (ground motion) response spectra (SSRS) on the seismic design of the ACB and potential benefits that could be gained by considering spatial incoherence of seismic input motions.Maximum seismic response values for selected response parameters of interest were generated with both SSRS-compatible coherent and incoherent seismic input motions. Comparisons were made of the corresponding maximum response parameter values and in-structure (acceleration) response spectra (ISRS) generated for both the coherent and incoherent motion inputs. These comparisons indicate that, by incorporating incoherence of ground motions in the seismic input, the maximum response values reduces and the ISRS peak amplitudes in the high frequency range (>10Hz) also reduce from the corresponding response values resulting from the coherent motion input. The amount of ISRS-amplitude reduction increases as the spectral frequency increases, as expected. Such reductions can be as much as 20–50%. This case study demonstrates that, for a CEUS hard rock site where relatively high high-frequency in the seismic input response spectra exist, consideration of spatial incoherence of input motions would result in substantial benefits in reducing the high-frequency seismic responses. Such benefits are especially significant when a standard plant design is to be constructed at a CEUS hard rock site where the site-specific ground motion response spectra (GMRS) contain high high-frequency spectral contents.

Engineering vacuum-evacuated photonic states with three input beams and two detectors

From the explicit form of the probability amplitude for two cascade-placed beam splitters (with one squeezed state input and two coherent state inputs), we calculated the probability amplitude of the output beam as a function of the transmittance of the two beam splitters and the amplitude and the relative phase of the three input states. At a certain condition, the output beam had no vacuum and was in a highly nonclassical state that contained more than one photon. Armed with explicit probability amplitude for two beam splitters and two coherent states, the squeezed vacuum state might be a very useful tool for generating highly nonclassical light.

Quantum effects in the interaction of off-resonant coherent light with a single atom

Well controlled nonlinear interactions between light field pulses and single atoms could be used to implement optical quantum information technologies based on qubits encoded in superpositions of coherent states of light. Here, we investigate the transformation of a coherent light field input at a single atom sufficiently far from resonance to limit the decoherence effects associated with random excitations of the atom. The conditions for suppressing multi-photon scattering to implement arbitrarily large shifts of the coherent light amplitude without decoherence are studied. It is shown that quantum controlled coherent shifts can be achieved by sufficiently long coherent pulses, indicating the possibility of generating superpositions of coherent states with large amplitude differences. The dominant multi-photon scattering effect associated with four wave mixing is also identified, and the spectral and temporal characteristics of the entangled photon pairs generated by this process are discussed.

Computer simulations of synchrony and oscillations evoked by two coherent inputs

Coherent oscillations have been reported in multiple cortical areas. This study examines the characteristics of output spikes through computer simulations when the neural network model receives periodic/aperiodic spatiotemporal spikes with modulated/constant populational activity from two pathways. Synchronous oscillations which have the same period as the input are observed in response to periodic input patterns regardless of populational activity. The results confirm that the output frequency of synchrony is essentially determined by the period of the repeated input patterns. On the other hand, weak periodic outputs are observed when aperiodic spikes are input with modulated populational activity. In this case, higher firing rates are necessary to input for higher frequency oscillations. The spike-timing-dependent plasticity suppresses the spikes which do not contribute to the synchrony for periodic inputs. This effect corresponds to the experimental reports that learning sharpens the synchrony in the motor cortex. These results suggest that spatiotemporal spike patterns should be entrained on modulated populational activity to transmit oscillatory information effectively in the convergent pathway.

Efficient generation and multiplexing of optical orbital angular momentum modes in a ring fiber by using multiple coherent inputs

We propose an approach to efficiently generate and multiplex optical orbital angular momentum (OAM) modes in a fiber with a ring refractive index profile by using multiple coherent inputs from a Gaussian mode. By controlling the phase relationship of the multiple inputs, one can selectively generate OAM modes of different states l. By controlling both the amplitude and phase of the multiple inputs, multiple OAM modes can be generated simultaneously without additional loss coming from multiplexing. We show, by simulation, the generation of OAM modes (OAM state |l|<3) with mode purity greater than 99%. The power loss of generating and multiplexing seven modes is about 35%. A transmitter for an OAM-based mode-division multiplexing system is proposed based on the discrete Fourier transform between the data carried by the multiple inputs and the data carried by the OAM modes. The experimental implementation of the proposed approach could be achieved by integrating ring fiber, multicore fiber, and photonic integrated circuit technology.

Effect of losses on the performance of an SU(1,1) interferometer

We study the effect of losses on the phase sensitivity of the SU(1,1) interferometer for different configurations. We find that this type of interferometer is robust against losses that result from an inefficient detection system. This type of loss only introduces an overall prefactor to the sensitivity but does not change the $1/n$ scaling, where $n$ is the average number of particles inside the interferometer, characteristic of the Heisenberg limit. In addition, we show that under some conditions the SU(1,1) interferometer with coherent state inputs is also robust against internal losses. These results show that the SU(1,1) interferometer is a viable candidate for experimentally reaching the Heisenberg limit with current technology. Possible implementations of this interferometer using four-wave mixing in atomic vapors or an atom interferometer in a spinor Bose-Einstein condensate are compared.

A prediction method for separating and quantifying noise contributions from casings and other plate like components in complex machines

In the context of noise source identification in machines, sound intensity, pressure or velocity distributions on a plane in space are commonly provided by intensity or holography maps. These maps, however, are not capable of separating the sources that are located on different planes, e.g. machines' radiating casings versus internal noise sources. The method discussed in this paper has been developed to analyze such situations. It consists of multiple partially coherent inputs–single output modeling to predict the radiations generated by machine casings or other plate like components. A parallel analysis with intensity will then enable to separate the casing or plate contribution from those of the internal sources. The application of this technique must, however, be accompanied by tools that allow to check its validity. Several of such tools are suggested. The method applications and validity checks have been discussed for a grinder wheel guard and a panel saw's blade casing.

A Fourier Based Method for Approximating the Joint Detection Probability in MIMO Communications

We propose a numerically efficient technique to approximate the joint detection probability of a coherent multiple input multiple output (MIMO) receiver in the presence of inter-symbol interference (ISI) and additive white Gaussian noise (AWGN). This technique approximates the probability of detection by numerically integrating the product of the characteristic function (CF) of the received filtered signal with the Fourier transform of the multi-dimension decision region. Naturally, the accuracy of the approximation is dependent on the number of points in the numerical integration. The proposed method selects the number of points to integrate over by deriving bounds on the approximation error. As such, a reduction of up to 1/100th of the number points can be achieved when comparing with existing single input single output (SISO) techniques. Simulation results demonstrate that the proposed method is highly accurate with the calculated errors being well within the bounded approximation error. In addition, the results are closely matched with those obtained using the Monte Carlo simulations with a typical error less than 10-4 while requiring only a fraction of the computation time.

Perfect Absorption of Light by Coherently Induced Plasmon Hybridization in Ultrathin Metamaterial Film

We demonstrated numerically that light can be totally absorbed by an ultrathin metamaterial film through coherently induced plasmon hybridization. Two fundamental modes, namely symmetrical and antisymmetrical modes, are observed in the metal–insulator–metal structure and attributed to the electric and magnetic resonance, respectively. Each kind of resonance is related to a distinct absorption peak for the corresponding coherent inputs. In particular, it is found that the antisymmetrical absorption is almost omnidirectional and suitable for divergent beams with arbitrary polarization and angle of incidence. To interpret the interaction of magnetic and electric fields with the structure, effective material parameters of the metamaterial are also retrieved, showing good agreement with the intuitive discussion. Furthermore, the general condition of coherent perfect absorption in a metamaterial thin film is given, which could be helpful for the design and understanding of such absorbers.

Spin-to-Orbital Angular Momentum Conversion and Spin-Polarization Filtering in Electron Beams

We propose the design of a space-variant Wien filter for electron beams that induces a spin half-turn and converts the corresponding spin angular momentum variation into orbital angular momentum of the beam itself by exploiting a geometrical phase arising in the spin manipulation. When applied to a spatially coherent input spin-polarized electron beam, such a device can generate an electron vortex beam, carrying orbital angular momentum. When applied to an unpolarized input beam, the proposed device, in combination with a suitable diffraction element, can act as a very effective spin-polarization filter. The same approach can also be applied to neutron or atom beams.

A Facilitated Interface to Generate a Combined Textual and Graphical Database System Using Widely Available Software

Data-Base Management System (DBMS) is the current standard for storing information. A DBMS organizes and maintains a structure of storage of data. Databases make it possible to store vast amounts of randomly created information and then retrieve items using associative reasoning in search routines. However, design of databases is cumbersome. If one is to use a database primarily to directly input information, each field must be predefined manually, and the fields must be organized to permit coherent data input. This static requirement is problematic and requires that database table(s) be predefined and customized at the outset, a difficult proposition since current DBMS lack a user friendly front end to allow flexible design of the input model. Furthermore, databases are primarily text based, making it difficult to process graphical data. We have developed a general and nonproprietary approach to the problem of input modeling designed to make use of the known informational architecture to map data to a database and then retrieve the original document in freely editable form. We create form templates using ordinary word processing software: Microsoft InfoPath 2007. Each field in the form is given a unique name identifier in order to be distinguished in the database. It is possible to export text based documents created initially in Microsoft Word by placing a colon at the beginning of any desired field location. InfoPath then captures the preceding string and uses it as the label for the field. Each form can be structured in a way to include any combination of both textual and graphical fields. We input data into InfoPath templates. We then submit the data through a web service to populate fields in an SQL database. By appropriate indexing, we can then recall the entire document from the SQL database for editing, with corresponding audit trail. Graphical data is handled no differently than textual data and is embedded in the database itself permitting direct query approaches. This technique makes it possible for general users to benefit from a combined text-graphical database environment with a flexible non-proprietary interface. Consequently, any template can be effortlessly transformed to a database system and easily recovered in a narrative form.

Demonstration of a Controlled-Phase Gate for Continuous-Variable One-Way Quantum Computation

We experimentally demonstrate a controlled-phase gate for continuous variables using a cluster-state resource of four optical modes. The two independent input states of the gate are coupled with the cluster in a teleportation-based fashion. As a result, one of the entanglement links present in the initial cluster state appears in the two unmeasured output modes as the corresponding entangling gate acting on the input states. The genuine quantum character of this gate becomes manifest and is verified through the presence of entanglement at the output for a product two-mode coherent input state. By combining our gate with the recently reported module for single-mode Gaussian operations [R. Ukai et al., Phys. Rev. Lett. 106, 240504 (2011)], it is possible to implement any multimode Gaussian operation as a fully measurement-based one-way quantum computation.

Quantum correlations by four-wave mixing in an atomic vapor in a nonamplifying regime: Quantum beam splitter for photons

We study the generation of intensity quantum correlations using four-wave mixing in a rubidium vapor. The absence of cavity in these experiments allows to deal with several spatial modes simultaneously. In the standard, amplifying, configuration, we measure relative intensity squeezing up to 9.2 dB below the standard quantum limit. We also theoretically identify and experimentally demonstrate an original regime where, despite no overall amplification, quantum correlations are generated. In this regime a four-wave mixing set-up can therefore play the role of a photonic beam splitter with non--classical properties, i.e. a device that splits a coherent state input into two quantum correlated beams.

Fiber coupler for generating orbital angular momentum modes

We propose a fiber coupler consisting of a central ring and four external cores to generate up to ten orbital angular momentum (OAM) modes. Four coherent input lights are launched into the external cores and then coupled into the central ring waveguide to generate OAM modes. By changing the size of the external cores, one can selectively excite a high-order OAM mode. The quality of the generated OAM modes can be enhanced by adjusting the polarization state and the phase of input lights. We show the generation of OAM modes with odd charge numbers of -9 to +9 (i.e., 10 modes totally) with mode purity of >99% using <2 mm long fiber. This fiber coupler design can be extended to enable all-fiber spatial-mode (de)multiplexing.

Tradeoff between energy and error in the discrimination of quantum-optical devices

We address the problem of energy-error tradeoff in the discrimination between two linear passive quantum optical devices with a single use. We provide an analytical derivation of the optimal strategy for beamsplitters and an iterative algorithm converging to the optimum in the general case. We then compare the optimal strategy with a simpler strategy using coherent input states and homodyne detection. It turns out that the former requires much less energy in order to achieve the same performances.

脉冲微波式氢原子钟初步结果

Adequate coherent pulsed microwave input into microwave cavity of atomic clock can induce Ramsey fringes of the atomic transition. By which the line width of atomic clock can be greatly reduced and the performance might be improved. This method has been applied in the POP rubidium clock. Shanghai Astronomical Observatory, Chinese Academy of Sciences has studied the application of this method in passive hydrogen maser. The electrical circuit for the pulsed microwave frequency sweeping has been designed, and the Ramsey fringes of hydrogen atom have been observed, which means that this method for passive hydrogen maser is feasible. We plan to optimize the parameter of the system and microwave pulse to further reduce the line width. And the designed full-scale servo circuit realizes the pulsed microwave hydrogen maser. Finally the system performance will be measured and optimized.

Quantum process tomography with coherent states

We have developed an enhanced technique for characterizing quantum optical processes based on probing unknown quantum processes only with coherent states. Our method substantially improves the original proposal (Lobino et al 2008 Science 322 563), which uses a filtered Glauber–Sudarshan decomposition to determine the effect of the process on an arbitrary state. We introduce a new relation between the action of a general quantum process on coherent state inputs and its action on an arbitrary quantum state. This relation eliminates the need to invoke the Glauber–Sudarshan representation for states; hence, it dramatically simplifies the task of process identification and removes a potential source of error. The new relation also enables straightforward extensions of the method to multi-mode and non-trace-preserving processes. We illustrate our formalism with several examples, in which we derive analytic representations of several fundamental quantum optical processes in the Fock basis. In particular, we introduce photon-number cutoff as a reasonable physical resource limitation and address resource versus accuracy trade-off in practical applications. We show that the accuracy of process estimation scales inversely with the square root of photon-number cutoff.

Quantum interference between a single-photon Fock state and a coherent state

We derive analytical expressions for the single mode quantum field state at the individual output ports of a beam splitter when a single-photon Fock state and a coherent state are incident on the input ports. The output states turn out to be a statistical mixture between a displaced Fock state and a coherent state. Consequently we are able to find an analytical expression for the corresponding Wigner function. Because of the generality of our calculations the obtained results are valid for all passive and lossless optical four port devices. We show further how the results can be adapted to the case of the Mach–Zehnder interferometer. In addition we consider the case for which the single-photon Fock state is replaced with a general input state: a coherent input state displaces each general quantum state at the output port of a beam splitter with the displacement parameter being the amplitude of the coherent state.

Maturation of GABAergic Inhibition Promotes Strengthening of Temporally Coherent Inputs among Convergent Pathways

Spike-timing-dependent plasticity (STDP), a form of Hebbian plasticity, is inherently stabilizing. Whether and how GABAergic inhibition influences STDP is not well understood. Using a model neuron driven by converging inputs modifiable by STDP, we determined that a sufficient level of inhibition was critical to ensure that temporal coherence (correlation among presynaptic spike times) of synaptic inputs, rather than initial strength or number of inputs within a pathway, controlled postsynaptic spike timing. Inhibition exerted this effect by preferentially reducing synaptic efficacy, the ability of inputs to evoke postsynaptic action potentials, of the less coherent inputs. In visual cortical slices, inhibition potently reduced synaptic efficacy at ages during but not before the critical period of ocular dominance (OD) plasticity. Whole-cell recordings revealed that the amplitude of unitary IPSCs from parvalbumin positive (Pv+) interneurons to pyramidal neurons increased during the critical period, while the synaptic decay time-constant decreased. In addition, intrinsic properties of Pv+ interneurons matured, resulting in an increase in instantaneous firing rate. Our results suggest that maturation of inhibition in visual cortex ensures that the temporally coherent inputs (e.g. those from the open eye during monocular deprivation) control postsynaptic spike times of binocular neurons, a prerequisite for Hebbian mechanisms to induce OD plasticity.