Multi-cavity System Research Articles

Multi-target-qubit unconventional geometric phase gate in a multi-cavity system.

Cavity-based large scale quantum information processing (QIP) may involve multiple cavities and require performing various quantum logic operations on qubits distributed in different cavities. Geometric-phase-based quantum computing has drawn much attention recently, which offers advantages against inaccuracies and local fluctuations. In addition, multiqubit gates are particularly appealing and play important roles in QIP. We here present a simple and efficient scheme for realizing a multi-target-qubit unconventional geometric phase gate in a multi-cavity system. This multiqubit phase gate has a common control qubit but different target qubits distributed in different cavities, which can be achieved using a single-step operation. The gate operation time is independent of the number of qubits and only two levels for each qubit are needed. This multiqubit gate is generic, e.g., by performing single-qubit operations, it can be converted into two types of significant multi-target-qubit phase gates useful in QIP. The proposal is quite general, which can be used to accomplish the same task for a general type of qubits such as atoms, NV centers, quantum dots, and superconducting qubits.

Entangling superconducting qubits in a multi-cavity system

Important tasks in cavity quantum electrodynamics include the generation and control of quantum states of spatially separated particles distributed in different cavities. An interesting question in this context is how to prepare entanglement among particles located in different cavities, which are important for large-scale quantum information processing. We here consider a multi-cavity system where cavities are coupled to a superconducting (SC) qubit and each cavity hosts many SC qubits. We show that all intra-cavity SC qubits plus the coupler SC qubit can be prepared in an entangled Greenberger–Horne–Zeilinger (GHZ) state, by using a single operation and without the need of measurements. The GHZ state is created without exciting the cavity modes; thus greatly suppressing the decoherence caused by the cavity-photon decay and the effect of unwanted inter-cavity crosstalk on the operation. We also introduce two simple methods for entangling the intra-cavity SC qubits in a GHZ state. As an example, our numerical simulations show that it is feasible, with current circuit-QED technology, to prepare high-fidelity GHZ states, for up to nine SC qubits by using SC qubits distributed in two cavities. This proposal can in principle be used to implement a GHZ state for an arbitrary number of SC qubits distributed in multiple cavities. The proposal is quite general and can be applied to a wide range of physical systems, with the intra-cavity qubits being either atoms, NV centers, quantum dots, or various SC qubits.

Trapped modes and Fano resonances in two-dimensional acoustical duct–cavity systems

AbstractRevisiting the classical acoustics problem of rectangular side-branch cavities in a two-dimensional duct of infinite length, we use the finite-element method to numerically compute the acoustic resonances as well as the sound transmission and reflection for an incoming fundamental duct mode. To satisfy the requirement of outgoing waves in the far field, we use two different forms of absorbing boundary conditions, namely the complex scaling method and the Hardy space method. In general, the resonances are damped due to radiation losses, but there also exist various types of localized trapped modes with nominally zero radiation loss. The most common type of trapped mode is antisymmetric about the duct axis and becomes quasi-trapped with very low damping if the symmetry about the duct axis is broken. In this case a Fano resonance results, with resonance and antiresonance features and drastic changes in the sound transmission and reflection coefficients. Two other types of trapped modes, termed embedded trapped modes, result from the interaction of neighbouring modes or Fabry–Pérot interference in multi-cavity systems. These embedded trapped modes occur only for very particular geometry parameters and frequencies and become highly localized quasi-trapped modes as soon as the geometry is perturbed. We show that all three types of trapped modes are possible in duct–cavity systems and that embedded trapped modes continue to exist when a cavity is moved off centre. If several cavities interact, the single-cavity trapped mode splits into several trapped supermodes, which might be useful for the design of low-frequency acoustic filters.

Displacement of Salty Water by Fresh Water in the Presence of Marangoni Convection

This paper numerically investigates the interaction between the Marangoni convection, the double diffusive convection and the intrusion force a multi-cavity system. The model consists of a two-cavity rectangular system in which the smaller cavity is located at the top left corner of the larger one. The larger cavity is filled with hot salty fluid while the smaller one contains cold fresh fluid. This problem is solved for the case of the fresh water intruding into the salty water. The interaction between the Marangoni (thermal and solutal) and the double diffusive regimes is investigated, for different solutal Rayleigh number, in detail. Finite element modelling results indicate that salinity induces stronger convection than the thermal ones and the thermal and solutal Marangoni convection further enhances the strength of the cellular flow. Numerical results indicate that surface force should be taken into consideration during the analysis and that the intruding force played an important role in the flow behaviour.

Double diffusive and Marangoni convection in a multi-cavity system

This paper numerically investigates the interaction between the Marangoni and the double diffusive convection in the Maxworthy Journal of Fluid Mechanics,1983, 128, 259–282] set-up. The model consists of a two-cavity rectangular system in which the smaller cavity is located at the top left corner of the larger one. The larger cavity is filled with hot salty fluid while the smaller one contains cold fresh fluid. This problem is solved for two different cases: the first one contains a rigid upper cavity, thereby, eliminating the Marangoni effect, and the second one contains a free-surface upper cavity. For the latter case, the interaction between the Marangoni (thermal and solutal) and the double diffusive regimes is investigated in detail. Finite element modelling results indicate that salinity induces stronger convection than the thermal ones. For the case for which a free surface exists, thermal and solutal Marangoni convection further enhances the strength of the cellular flow. Numerical results agree qualitatively with the Maxworthy experiment. It is shown that the governing equations should be solved in the complete form and that the surface tension should be taken into consideration during the numerical analysis.

Macroparticle theory of a standing wave free-electron laser two-beam accelerator

Free-electron laser operation is formulated using a macroparticle approach based on a universal gain equation. Microwave excitation in a single cavity is derived analytically and is given in the form of analytic recursion equations for a multicavity system driven by a sequence of electron bunches. Qualitative and quantitative insights into the basic excitation and saturation mechanisms are provided. Stability analysis on a test particle moving around a macroparticle shows the importance of precise control of bunch spacing.

Quantum Theory of Electron-Cavity Interactions

The quantum-theoretic method developed in one of our earlier papers is applied to the interaction of an electron with a multicavity system. This analysis is extended to the two-cavity oscillator, linear accelerator (linac), and frequency mixer. It is found that the experimental observations done so far in the above systems do not depend on the quantum state of the cavity field. A comparison of the oscillator theory and the linac given here indicates that the weak-field limit should be taken as the correct classical limit according to the generalized correspondence principle. Finally, a possible refinement of linac design, as a result of the present calculation, is pointed out.

Studies in the development of high-power klystrons

A survey is given of the experience gained during the development of high-power klystron amplifiers, with reference to design principles, the application of getter pumps inside sealed-off valves, wide-band tuning mechanism, output windows, influence of secondary emission on tube performance, etc. Also, further experiments on broadbanding of multi-cavity amplifier systems are discussed.