Qubits ride the photon bus

Anonymous

S. D. Barrett, Gerard J Milburn

We describe a method to perform two-qubit measurements and logic operations on pairs of qubits which each interact with a harmonic oscillator degree of freedom (the bus), but do not directly interact with one another. Our scheme uses only weak interactions between the qubit and the bus, homodyne measurements, and single-qubit operations. In contrast to earlier schemes, the technique presented here is extremely robust to photon loss in the bus mode, and can function with high fidelity even when the rate of photon loss is comparable to the strength of the qubit-bus coupling.

Gui-Long Gao, Fuquan Song, Shou-Sheng Huang +4 more

We propose an effective method to produce four-qubit χ-type entangled states by using flux qubits coupled to an LC circuit which acts as a quantum data bus (QDB). In our scheme, the interaction is mediated by the exchange of virtual rather than real photons because of the large detuning between flux qubits and QDB, and then QDB-induced loss can be effectively avoided. The experimental feasibility of the scheme is also presented.

Bettina Just

Jin‐Xuan Han, Jin‐Lei Wu, Yan Wang +3 more

We propose a one-step scheme for implementing multi-qubit phase gates on microwave photons in multiple resonators mediated by a superconducting bus in circuit quantum electrodynamics (QED) system. In the scheme, multiple single-mode resonators carry quantum information with their vacuum and single-photon Fock states, and a multi-level artificial atom acts as a quantum bus which induces the indirect interaction among resonators. The method of pulse engineering is used to shape the coupling strength between resonators and the bus so as to improve the fidelity and robustness of the scheme. We also discuss the influence of finite coherence time for the bus and resonators on gate fidelity respectively. Finally, we consider the suppression of unwanted transitions and propose the method of optimized detuning compensation for offsetting unwanted transitions, showing the feasibility of the scheme within the current experiment technology.

Ahmed El-Halawany, Michael Leuenberger