Preparation of macroscopic quantum superposition states of a cavity field via coupling to a superconducting charge qubit

We propose how to generate macroscopic quantum superposition states using a microwave cavity containing a superconducting charge qubit. Based on the measurement of charge states, we show that the superpositions of two macroscopically distinguishable coherent states of a single-mode cavity field can be generated by a controllable interaction between a cavity field and a charge qubit. After such superpositions of the cavity field are created, the interaction can be switched off by the classical magnetic field, and there is no information transfer between the cavity field and the charge qubit. We also discuss the generation of the superpositions of two squeezed coherent states.

Figure 1

Rabi frequency $\mid \Omega \mid$ versus the microwave wavelength $\lambda$ for a full-wavelength cavity (a) and a quarter-wavelength cavity (b) with ratios $E_{\mathrm{ch}}∕E_{\mathrm{J}}=4$ (top solid line), 7 (dashed line), 10 (dash-dotted line), and 15 (bottom dotted line), respectively.