Logical states for fault-tolerant quantum computation with propagating light.

To harness the potential of a quantum computer, quantum information must be protected against error by encoding it into a logical state that is suitable for quantum error correction. The Gottesman-Kitaev-Preskill (GKP) qubit is a promising candidate because the required multiqubit operations are readily available at optical frequency. To date, however, GKP qubits have been demonstrated only at mechanical and microwave frequencies. We realized a GKP state in propagating light at telecommunication wavelength and verified it through homodyne measurements without loss corrections. The generation is based on interference of cat states, followed by homodyne measurements. Our final states exhibit nonclassicality and non-Gaussianity, including the trident shape of faint instances of GKP states. Improvements toward brighter, multipeaked GKP qubits will be the basis for quantum computation with light.

Nonlinear feedforward enabling quantum computation.

Measurement-based quantum computation with optical time-domain multiplexing is a promising method to realize a quantum computer from the viewpoint of scalability. Fault tolerance and universality are also realizable by preparing appropriate resource quantum states and electro-optical feedforward that is altered based on measurement results. While linear feedforward has been realized and become a common experimental technique, nonlinear feedforward was unrealized until now. In this paper, we demonstrate that a fast and flexible nonlinear feedforward realizes the essential measurement required for fault-tolerant and universal quantum computation. Using non-Gaussian ancillary states, we observed 10% reduction of the measurement excess noise relative to classical vacuum ancilla.

Extending the piezoelectric transducer bandwidth of an optical interferometer by suppressing resonance using a high dimensional IIR filter implemented on an FPGA.

This paper considers the application of Field Programmable Gate Array (FPGA)-based infinite impulse response (IIR) filtering to increase the usable bandwidth of a piezoelectric transducer used in optical phase locking. We experimentally perform system identification of the interferometer with the cross-correlation method integrated on the controller hardware. Our model is then used to implement an inverse filter designed to suppress the low frequency resonant modes of the piezoelectric transducer. This filter is realized as a 24th-order IIR filter on the FPGA, while the total input-output delay is kept at 350 ns. The combination of the inverse filter and the piezoelectric transducer works as a nearly flat response position actuator, allowing us to use a proportional-integral (PI) control in order to achieve stability of the closed-loop system with significant improvements over a non-filtered PI control. Finally, because this controller is completely digital, it is straightforward to reproduce. Our control scheme is suitable for many experiments that require highly accurate control of flexible structures.

Experimental validation of spatial Fourier transform-based multiple sound zone generation with a linear loudspeaker array.

Generating acoustically bright and dark zones using loudspeakers is gaining attention as one of the most important acoustic communication techniques for such uses as personal sound systems and multilingual guide services. Although most conventional methods are based on numerical solutions, an analytical approach based on the spatial Fourier transform with a linear loudspeaker array has been proposed, and its effectiveness has been compared with conventional acoustic energy difference maximization and presented by computer simulations. To describe the effectiveness of the proposal in actual environments, this paper investigates the experimental validation of the proposed approach with rectangular and Hann windows and compared it with three conventional methods: simple delay-and-sum beamforming, contrast maximization, and least squares-based pressure matching using an actually implemented linear array of 64 loudspeakers in an anechoic chamber. The results of both the computer simulations and the actual experiments show that the proposed approach with a Hann window more accurately controlled the bright and dark zones than the conventional methods.

Nuclear export of influenza viral ribonucleoprotein is temperature-dependently inhibited by dissociation of viral matrix protein.

The influenza virus copies its genomic RNA in the nuclei of host cells, but the viral particles are formed at the plasma membrane. Thus, the export of new genome from the nucleus into the cytoplasm is essential for viral production. Several viral proteins, such as nucleoprotein (NP) and RNA polymerases, synthesized in the cytoplasm, are imported into the nucleus, and form viral ribonucleoprotein (vRNP) with new genomic RNA. vRNP is then exported into the cytoplasm from the nucleus to produce new viral particles. M1, a viral matrix protein, is suggested to participate in the nuclear export of vRNP. It was found unexpectedly that the production of influenza virus was suppressed in MDCK cells at 41 degrees C, although viral proteins were synthesized and the cytopathic effect was observed in host cells. Indirect immunofluorescent staining with anti-NP or M1 monoclonal antibody showed that NP and M1 remained in the nuclei of infected cells at 41 degrees C, suggesting that a suppression of viral production was caused by inhibition of the nuclear export of these proteins. The cellular machinery for nuclear export depending on CRM1, which mediates the nuclear export of influenza viral RNP, functioned normally at 41 degrees C. Glycerol-density gradient centrifugation demonstrated that vRNP also formed normally at 41 degrees C. However, an examination of the interaction between vRNP and M1 by immunoprecipitation indicated that M1 did not associate with vRNP at 41 degrees C, suggesting that the association is essential for the nuclear export of vRNP. Furthermore, when infected cells incubated at 41 degrees C were cultured at 37 degrees C, the interaction between vRNP and M1 was no longer detected even at 37 degrees C. The results suggest that M1 synthesized at 41 degrees C is unable to interact with vRNP and the dissociation of M1 from vRNP is one of the reasons that the transfer of vRNP into the cytoplasm from the nucleus is prevented at 41 degrees C.