Chun-Wang Wu

Scalable one-way quantum computer using on-chip resonator qubits

College of Science, National University of Defense Technology, Changsha 410073, People’s Republic of China(Dated: November 14, 2011)We propose a scalable and robust architecture for one-way quantum computation using couplednetworks of superconducting transmission line resonators. In our protocol, quantum information isencoded into the long-lived photon states of the resonators, which have a much longer coherencetime than the usual superconducting qubits. Each resonator contains a charge qubit used for thestate initialization and local projective measurement of the photonic qubit. Any pair of neighboringphotonic qubits are coupled via a mediator charge qubit, and large photonic cluster states can becreated by applying Stark-shifted Rabi pulses to these mediator qubits. The distinct advantage ofour architecture is that it combines both the excellent scalability of the solid-state systems and thelong coherence time of the photonic qubits. Furthermore, this architecture is very robust againstthe parameter variations.

Performance of a cooling method by quadratic coupling at high temperatures

We consider the radiative trapping and cooling of a partially reflecting mirror suspended inside an optical cavity, generalizing the case of a perfectly reflecting mirror previously considered [M. Bhattacharya and P. Meystre, Phys. Rev. Lett. 99, 073601 (2007)]. This configuration was recently used in an experiment to cool a nanometers-thick dielectric membrane [J. D. Thompson et al., e-print arXiv:0707.1724v2]. The self-consistent cavity field modes of this system depend strongly on the position of the middle mirror, leading to important qualitative differences in the radiation pressure effects: in one case, the situation is similar to that of a perfectly reflecting middle mirror, with only minor quantitative modifications. In addition, we also identify a range of mirror positions for which the radiation-mirror-coupling becomes purely dispersive and the back-action effects that usually lead to cooling are absent, although the mirror can still be optically trapped. The existence of these two regimes leads us to propose a bichromatic scheme that optimizes the cooling and trapping of partially reflective mirrors.

Quantum superposition of localized and delocalized phases of photons

Abstract Based on a variant of 2-site Jaynes–Cummings–Hubbard model constructed using superconducting circuits, we propose a method to coherently superpose the localized and delocalized phases of microwave photons, which makes it possible to engineer the collective features of multiple photons in the quantum way using an individual two-level system. Our proposed architecture is also a promising candidate for implementing distributed quantum computation since it is capable of coupling remote qubits in separate resonators in a controllable way.