Detecting non-Abelian geometric phase in circuit QED

We propose a scheme for detecting noncommutative feature of the non-Abelian geometric phase in circuit QED, which involves three transmon qubits capacitively coupled to an one-dimensional transmission line resonator. By controlling the external magnetic flux of the transmon qubits, we can obtain an effective tripod interaction of our circuit QED setup. The noncommutative feature of the non-Abelian geometric phase is manifested that for an initial state undergo two specific loops in different order will result in different final states. Our numerical calculations show that this difference can be unambiguously detected in the proposed system.     

Simulation of the Majorana equation in circuit QED

We propose a scheme to simulate the 1D Majorana equation with two Cooper pair boxes coupled to a 1D superconducting transmission line resonator, where strong coupling limit can be achieved. With proper choice of systematic parameters, we are able to engineer different kind of interactions, which are indispensable for simulating the Majorana equation in an enlarged real Hilbert space. Measurement of a conserved observable, i.e., the pseudo-helicity, via transmission spectrum of the cavity field can verify the simulated Majorana wave function. The measurement is experimentally resolvable according to our estimation based on conservative experimental parameters.     

Quantum parameter estimation via dispersive measurement in circuit QED

Quantum Information Processing - Quantum key distribution is one of the most fundamental cryptographic protocols. Quantum walks are important primitives for computing. In this paper, we take...     

Tunable interaction of superconducting flux qubits in circuit QED

We propose to implement tunable interaction of superconducting flux qubits with cavity-assisted interaction and strong driving. The qubits have a three-level Lambda configuration, and the decay of the excited state will be greatly suppressed due to the effective large detuning. The implemented interaction is insensitive to the cavity field state and can be controlled by modulating the phase difference of the driving fields of the qubits. In particular, our scheme is based on the typical circuit QED setup and thus will provide a simple method towards the tunable interaction of superconducting qubits. Finally, we consider the generation of two and four qubits entangled states with the constructed interaction under the influence of typical decoherence effects.     

Fast geometric gate operation of superconducting charge qubits in circuit QED

A scheme for coupling superconducting charge qubits via a one-dimensional superconducting transmission line resonator is proposed. The qubits are working at their optimal points, where they are immune to the charge noise and possess long decoherence time. Analysis on the dynamical time evolution of the interaction is presented, which is shown to be insensitive to the initial state of the resonator field. This scheme enables fast gate operation and is readily scalable to multiqubit scenario.     

One-step quantum phase gate in the ultrastrong coupling regime of circuit QED

In a previous publication (Phys Rev Lett 108: 120501, 2012), Romero et al. proposed an ultrastrong coupling circuit QED system that can implement a two-qubit quantum phase gate with four controlling pulses. Based on this architecture, we demonstrate that an ultrafast two-qubit phase gate can also be realized with only one oscillation and lower coupling strengths. In our operation scheme, two identical qubits evolve synchronously under a single pulse with a duration determined by a specific coupling strength. The phase gate can also be obtained periodically. The influences of parameter fluctuations are estimated. We demonstrate that the fidelities can be greater than 99% if the parameter fluctuations are controlled within 5%.     

Two-mode multi-partitioning

New methodologies for two-mode (objects and variables) multi-partitioning of two way data are presented. In particular, by reanalyzing the double k-means, that identifies a unique partition for each mode of the data, a relevant extension is discussed which allows to specify more partitions of one mode, conditionally to the partition of the other one. The performance of such generalized double k-means has been tested by both a simulation study and an application to gene microarray data.     

One-step implementation of a multi-target-qubit controlled phase gate in a multi-resonator circuit QED system

Circuit quantum electrodynamics system composed of many qubits and resonators may provide an excellent way to realize large-scale quantum information processing (QIP). Because of key role for large-scale QIP and quantum computation, multi-qubit gates have drawn intensive attention recently. Here, we present a one-step method to achieve a multi-target-qubit controlled phase gate in a multi-resonator system, which possesses a common control qubit and multiple different target qubits distributed in their respective resonators. Noteworthily, the implementation of this multi-qubit phase gate does not require classical pulses, and the gate operation time is independent of the number of qubits. Besides, the proposed scheme can in principle be adapted to a general type of qubits like natural atoms, quantum dots, and solid-state qubits (e.g., superconducting qubits and NV centers).     

Spatial Decoherence in QED

We consider the dynamics of a charged free particle, initially described by a coherent wave packet, interacting with an electromagnetic field characterized by the temperature T, considered as the environment. We have used dipole approximation neglecting the potential vector quadratic term in the minimal coupling Hamiltonian. This leads to the loss of coherence in the momentum representation, described by the decay of the off diagonal elements of the particle reduced density matrix, while the populations remain constant. Here we extend the analysis to the coordinate representation. We compute the particle reduced density matrix in this basis, analyzing in particular the mixing of various effects, such as free spreading, vacuum dressing and vacuum and thermal decoherence, in the wave packet width and coherence length evolution.     

Two-mode Gaussian product states in a lossy interferometer

The quantum Fisher information for a two-mode, Gaussian product state in an interferometer subject to photon loss is studied. We obtain the quantum Cramer–Rao bound on the achievable precision in phase estimation using such states. The scaling of the measurement precision with the mean photon number is compared to the shot noise-limited scaling for dual squeezed vacuum states and dual squeezed, displaced vacuum states.     

Particle squeezing in narrow confinements

Many lab-on-a-chip applications require processing of droplets, cells, and particles using narrow confinements. The physics governing the process of a particle squeezing through narrow confinement is complex. Various models and applications have been developed in this area in recent years. In the present paper, we review the physics, modeling approaches, and designs of narrow confinements for the control of deformable droplets, cells, and particles. This review highlights the interdisciplinary nature of the problem, since the experimental, analytical, and numerical methods used in studies of particle squeezing through narrow confinements come from various fields of science and technology.     

Two-mode ILC with pseudo-downsampled learning in high frequency range

In this paper, an iterative learning control scheme that combines the designs in the frequency and time domains is proposed to improve the tracking accuracy. The scheme separates the error signals into low and high frequency band error components and employs different learning mechanisms to deal with these error components, respectively. On the low frequency band, a conventional iterative learning control is used. On the high frequency band, a downsampled learning is implemented to suppress more error components to generate a high tracking accuracy. We will address in detail the issues of signal separation, learning controller design, convergence analysis, and experimental verification of the proposed scheme.     

Scaled control in the QED regime

We develop many-server asymptotics in the Quality-and-Efficiency-Driven (QED) regime for models with admission control. The admission control, designed to reduce the incoming traffic in periods of congestion, scales with the size of the system. For a class of Markovian models with this scaled control, we identify the QED limits for two stationary performance measures. We also derive corrected QED approximations, generalizing earlier results for the Erlang B, C and A models. These results are useful for the dimensioning of large systems equipped with an active control policy. In particular, the corrected approximations can be leveraged to establish the optimality gaps related to square-root staffing and asymptotic dimensioning with admission control.     

Quantum Cloning and Cavity QED

A Universal 1 → 2 Cloner is proposed using cavity QED. This is a deterministic proposal that takes far less steps than previous models, and makes use of dispersive C-NOT gates.Presented at the International Conference ‘Entanglement, Information & Noise’, Krzyżowa, Poland, June 14-20, 2004.     

Two-mode control: an oculomotor-based approach to tracking systems

The paper aims to use the knowledge about how the visual system organizes the components of oculomotor system to propose a new tracking paradigm. The tracking system is assumed to be described by linear time-invariant discrete-time state-space equations. The approach described, motivated by the behavior of the visual system, is to switch off the smooth controller whenever a violation occurs and design a time-optimal control action, i.e., a “saccade”, to drive the control system so that the constraint is satisfied after the shortest possible time interval. After that, the smooth controller is switched back into the loop. The way this switching is performed is critical for obtaining “good behavior”. A method is proposed which is based on a careful definition of the target set for the saccade. The tracking system proposed in this paper is closely related to recent results in linear optimal and robust control theory     

New squeezing mechanisms for L systems

Some new mechanisms for defining the language of a given L system are introduced. In the production-universal (resp. production-existential) definition of the language, only those words are accepted which possess a derivation such that at the last step every production (resp. at least one production) applied belongs to a specific set of “good” productions. Both the production-universal and production-existential definition of the language are special cases of the more general production-subset definition. One is led naturally to these definitions if one wants to consider only certain stages in the development. Similar considerations lead to two other definitional mechanisms, namely, to the letter-universal and letter-existential definition. The paper investigates the mutual relationship between these mechanisms. It turns out that if the underlying L structure is strong enough (such as a TOL structure), then all of these definitional mechanisms are of equal power, whereas uncomparability and strict inclusion results are obtained for weaker underlying L structures.     

Droplet formation by squeezing in a microfluidic cross-junction

In microfluidics, flow focusing is widely used to produce water-in-oil droplets in microchannels at high frequency. We here report an experimental study of droplet formation in a microfluidic cross-junction with a minimum number of geometrical parameters. We mostly focus on the squeezing regime, which is composed of two distinct steps: filling and pinching. The duration of each step (and corresponding volumes of each liquid phase) is analyzed. They vary according to both water and oil flow rates. These variations provide several insights about the fluid flows in both phases. We propose several scaling laws to relate the droplet volume and frequency to the flow rate of both phases. We also discuss the influence of surfactant and channel compliance on droplet formation.     

Two-mode target selection: Considering target layouts in small touch screen devices

A variety of studies have been conducted to improve methods of selecting a tiny virtual target on small touch screen interfaces of handheld devices such as mobile phones and PDAs. These studies, however, focused on a specific selection method, and did not consider various layouts resulting from different target sizes and densities on the screen. This study proposes a Two-Mode Target Selection (TMTS) method that automatically detects the target layout and changes to an appropriate mode using the concept of an activation area. The usability of TMTS was compared experimentally to those of other methods. TMTS changed to the appropriate mode successfully for a given target layout and showed the shortest task completion time and the fewest touch inputs. TMTS was also rated by the users as the easiest to use and the most preferred. TMTS could significantly increase the ease, accuracy, and efficiency of target selection, and thus enhance user satisfaction when the users select targets on small touch screen devices.

Relevance to Industry

The results of this study can be used to develop fast and accurate target selection methods in handheld devices with touch screen interfaces especially when the users use their thumb to activate the desired target.     

电路计算机辅助设计系统中电路图的处理

介绍如何使用数据库技术来处理电路图问题。即将电路图中的每一个元器件的名称、位置、大小和使用图片等属性保存在数据库表的一条记录里,对每个元器件的修改其实就是修改数据库里对应记录的内容,这样电路图中的元器件都能以分离元件的形式分别进行移动、删除和保存。程序结果表明,使用数据库技术来处理电路图,可以很方便地对各个元器件进行调整,而且保存后,以后还可以任意调整。