Hybrid Receiver for QPSK Signals

01.02.2014, 17:28

Newsletter 5

 

One of the most profound consequences of quantum mechanics is the impossibility of constructing a device that can perfectly discriminate between non-orthogonal quantum states. This result is of particular relevance in the field of optical communications, where information is typically encoded in coherent states. In the case of low signal power, as for instance after the influence of loss in optical fibers, these states exhibit significant non-orthogonality, ultimately limiting the channel capacity. In current-day networks a widely used encoding technique is four partite quadrature phase-shift keying (QPSK). The corresponding standard receiver is a heterodyne detector that obtains information about the signals in the continuous variable basis, which can be related to the wave-like properties of the quantum state. We were able to show experimentally that a hybrid receiver, which additionally retrieves information in the discrete particle-like basis, can achieve error probabilities below the heterodyne limit for any signal power. The receiver initially performs a homodyne detection on part of the state. The information gained is fed forward to a displacement stage prior to being finally identified by a click detector.

 

Contact: christian.mueller(at)mpl.mpg(dot)de
Group: Leuchs Division
Reference: C. R. Müller et al., New J. Phys. 14, 083009 (2012).