A record-size quantum computing register

LC13841

- Quantum computing holds the revolutionary promise of exponentially speeding up such calculations as integer factoring and the simulation of quantum mechanical systems. Building a practical quantum computer will require a scalable number of individual quantum memory units ("Qbits" or "Qmodes"), all individually addressable and controllable with no error. In this paper, we demonstrated an experimental breakthrough: the generation of a record-size quantum register of 60 Qmodes, in 15 independently entangled (i.e. specifically correlated) sets, called cluster states. This massively scalable implementation of a quantum register was all-optical and based on an exotic laser, an optical parametric oscillator, which emitted quantum electromagnetic fields (the Qmodes) at equally spaced optical frequencies over an "optical frequency comb." Technical constraints limited the measured number of generated Qmodes to the reported 60 but we estimated the actual size of our quantum register to be of 180 to 600 Qmodes. This work is a major step toward entangling all these Qmodes together in a single cluster state, in order to achieve a scalable platform for a quantum computer.

Time-reversed optical parametric oscillation

LC13088

- The invention of the antilaser has attracted recently a considerable
attention from the scientific community and general media as well. The
antilaser is a device that acts like a laser in reverse and is thus
capable of completely absorbing coherent light beams instead of
scattering them as most other things do. Such a device might provide a
way to build miniature silicon optical switches or lead to new types
of photonic sensors.

In this Letter the author has shown rather generally that the main
idea of time-reversing a laser to perfectly annihilate coherent light
quanta is not peculiar to a laser system, and can be applied to other
kinds of optical instabilities. In particular, the time-reversed
process of optical parametric oscillation in a nonlinear crystal can
realize a kind of coherent perfect absorber for colored incident
signal and idler fields. In this device, two coherent light waves of
different colours can be fully annihilated in the crystal. As compared
to the antilaser, here photons are not converted into heat or some
internal energy of the medium, rather they are converted into photons
of a different colour. The idea of time reversing a generic kind of
optical instability is expected to be fruitful to built up a novel
class of optical devices similar to the antilaser but operating with
e.g. multicoloured light.