Here is my arxiv reading list for March 2019. New preprints this month reported breakthroughs in continuous variable quantum computation (Walshe et al. and Asavanant et al.); an almost perfect quantum-dot based photon-pair source by Wang et al.; and surprising theory that noise can induce amplification in bosonic channels by Chia et al.
Eaton, M., Nehra, R., & Pfister, O. arXiv:1903.01925. Gottesman-Kitaev-Preskill state preparation by photon catalysis.
A procedure to construct useful continuous variable states using photon catalysis. Photon catalysis is the interference of coherent states with single-photon states followed by post-selection using photon-number-resolved detection. With these tools, the preprint provides schemes to construct exact displaced single-photon states, squeezed cat states, and Gottesman-Kitaev-Preskill states.
Walshe, B. W., Mensen, L. J., Baragiola, B. Q., & Menicucci, N. C. arXiv:1903.02162. Robust fault tolerance for continuous-variable cluster states with excess anti-squeezing.
Thermal squeezed states are as good as vacuum squeezed states for fault-tolerance in continuous variable (CV) quantum computing. This preprint generalizes the important earlier result that CV cluster states created from squeezed vacuum states can be used for fault-tolerant quantum computation. Thermal states introduce an anti-squeezing, which could have led to much more stringent squeezing requirements for fault tolerance, but this does not happen: the 20.5 dB squeezed-vacuum threshold works just as well for the squeezed thermal states.
Asavanant, W., Shiozawa, Y., Yokoyama, S., Charoensombutamon, B., Emura, H., Alexander, R. N., Takeda, S., Yoshikawa, J., Menicucci, N. C., Yonezawa, H., & Furusawa, A. arXiv:1903.03918. Time-Domain Multiplexed 2-Dimensional Cluster State: Universal Quantum Computing Platform.
Experimental generation of a 5X5000 node two-dimensional CV cluster state. This experiment uses time-multiplexing, i.e., reusing spatial modes in time, to generate the states. In an incredible feat of stabilization, time multiplexing is performed with a 12m free-space delay line and a 40m optical fiber in the setup.
Wang, H., Hu, H., Chung, T.-H., Qin, J., Yang, X., Li, J.-P., Liu, R.-Z., Zhong, H.-S., He, Y.-M., Ding, X., Deng, Y.-H., Schneider, C., Dai, Q., Huo, Y.-H., HÃ¶fling, S., Lu, C.-Y., & Pan, J.-W. arXiv:1903.06071. On-demand semiconductor source of entangled photons which simultaneously has high fidelity, efficiency, and indistinguishability.
Deterministic source if entangled photon pairs. The source uses resonant excitation of quantum dot in a bullseye cavity. The specs are remarkable: entanglement fidelity is 90%, pair generation rate 59%, pair extraction efficiency 62%, and photon indistinguishability of 90% (93%) without (with) temporal filtering.
Experimental demonstration of dephasing in different basis effecting states differently. GHZ and cluster states respond differently to noise in the computational (0/1) and the transverse (+/-) basis. Specifically, the entanglement decays exponentially fast with the size of a GHZ state under a dephasing noise in the computational basis. Dephasing noise is simulated on polarization qubits by applying individual phase flips on the photons; this aspect of the experimental design is ingenious.
Bosonic channel in which multiplicative noise can amplify an input signal. Surprising noise channel in which the noise induces an amplification of an input signal. The channel is modelled by a single bosonic oscillator coupled to a gain medium comprising two-level atoms that mediate two-photon transition. The amplification results from classical correlation between the internal noise source of the amplifier and the signal that is being amplified.
Self-phase modulation instead of parametric down conversion for continuous-wave squeezed vacuum light. Self-phase modulation, i.e., fully degenerate four-wave mixing, is an alternative to parametric down conversion that does not require light at twice the frequency. So far, squeezing via self-phase modulation was only observed in light pulses but this preprint reports the same in continuous wave light. Obtaining the squeezing required a careful control of the temperature to suppress the unwanted second harmonic generation process.