Measurement-induced continuous-variable quantum interactions

We propose feasible implementations of basic continuous-variable (CV) interactions (squeezer, parametric amplifier, and quantum nondemolition interaction) between light modes without the requirement for in-line nonlinear couplings in a strongly pumped optical medium. The method is based entirely on linear optics, homodyne detection, and off-line squeezed ancillary states and therefore represents the CV analog of the measurement-induced nonlinearity approach, previously used in single-photon qubit experiments to probabilistically implement a controlled-NOT gate.

Figure 1

Schematic setup of the measurement-induced squeezing operation. PBS, polarizing beam splitter; SQ, single-mode vacuum squeezer; PS, phase shifter; HOM, homodyne detection system; CD, coupling device; HWP, half-wave plate; and LO, local oscillator.

Figure 2

Schematic setup of the measurement-induced QND interaction with nonunity transfer gains. The abbreviations are explained in the caption text of Fig. 1.

Figure 3

Schematic setup for the measurement-induced QND interaction at a distance with nonunity transfer gain. The abbreviations are explained in the caption of Fig. 1.

Figure 4

Schematic setup for measurement-induced QND interaction with unity transfer gain, and the measurement-induced phase-insensitive amplifier. The abbreviations are explained in the caption of Fig. 1.