Seiji Armstrong, Jean-Francois Morizur, Jiri Janousek, Boris Hage, Nicolas Treps, Ping Koy Lam, Hans-A. Bachor
Entanglement between large numbers of quantum modes is the quintessential
resource for quantum information processing and future applications such as the
quantum internet. Conventionally the generation of multimode entanglement in
optics requires complex layouts of beam-splitters and phase shifters in order
to transform the input modes in to entangled modes. These networks need
substantial modification for every new set of entangled modes to be generated.
Further, the complexity grows rapidly with the number of entangled modes as the
number of detectors, phase locks and optical components needs to be increased.
Here we report on the highly efficient and versatile generation of various
multimode entangled states within one optical beam. By defining our modes to be
combinations of different spatial regions of the beam, we may use just one pair
of multi-pixel detectors and one local oscillator to measure an orthogonal set
of modes. The transformation of this set into a desired set of entangled modes
is calculated ahead of time via a programmable virtual network of
beam-splitters and phase shifters. The transformation is then applied during
detection in real time. This enables us to change the set of measured entangled
modes via software only, optimizing the network for the desired outputs without
modifying the optical setup. The virtual networks are fully equivalent to the
physical linear optics networks they are emulating. We show that up to N-mode
entanglement is measurable given just one pair of detectors each with N
photodiodes, and demonstrate N=2 up to N=8 modes here. Our approach introduces
flexibility and scalability to multimode entanglement, two important attributes
that are presently lacking in state of the art devices.
View original:
http://arxiv.org/abs/1201.6024
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