Parallel generation of quadripartite cluster entanglement in the optical frequency comb.

Scalability and coherence are two essential requirements for the experimental implementation of quantum information and quantum computing. Here, we report a breakthrough toward scalability: the simultaneous generation of a record 15 quadripartite entangled cluster states over 60 consecutive cavity modes (Q modes), in the optical frequency comb of a single optical parametric oscillator. The amount of observed entanglement was constant over the 60 Q modes, thereby proving the intrinsic scalability of this system.

A new method for locking the signal-field phase difference in a type-II optical parametric oscillator above threshold.

We propose and demonstrate a new method for phaselocking the signal fields emitted above threshold by a nondegenerate, type-II optical parametric oscillator (OPO). This method is based on the observation that amplitude modulation of the pump beam produces a related modulation of the frequency difference of the OPO signals via the temperature-tuning of the index of refraction in the nonlinear crystal. We successfully use pump modulation as a correction for phase-difference locking of the OPO signals and observe a 1 kHz beat note stable over more than 10 s, both figures solely limited by the measurement time.

Quasi-phase-matched concurrent nonlinearities in periodically poled KTiOPO(4) for quantum computing over the optical frequency comb.

We report the successful design and experimental implementation of three coincident nonlinear interactions, namely ZZZ (type 0), ZYY (type I), and YYZ/YZY (type II) second-harmonic generation of 780 nm light from a 1560 nm pump beam in a single, multigrating, periodically poled KTiOPO(4) crystal. The resulting nonlinear medium is the key component for making a scalable quantum computer over the optical frequency comb of a single optical parametric oscillator.

Broadband amplitude squeezing in a periodically poled KTiOPO4 waveguide.

We generated -2.2 dB of broadband amplitude squeezing at 1064 nm in a periodically poled KTiOPO4 (PPKTP) waveguide by coupling of the fundamental and second-harmonic cw fields. This is the largest amount of squeezing obtained to date in a KTP waveguide, limited by propagation losses.