Optimal quantum-programmable projective measurements with coherent states

Understand

We consider a device which can be programmed using coherent states of light to approximate a given projective measurement on an input coherent state.

• We provide and discuss three practical implementations of this programmable projective measurement device with linear optics, involving only balanced beam splitters and single photon threshold detectors.
• The three schemes optimally approximate any projective measurement onto a program coherent state in a non-destructive fashion.
• We further extend these to the case where there are no assumptions on the input state.