Enabling large-scale and high-speed quantum computation is a key to practical quantum computation. Continuous-variable approach in optical systems offer advantages in scalability and speed by leveraging their temporal degree of freedom and inherent large carrier frequency. In this paper, we investigate the generation and manipulation of quantum entanglement through a time-domain multiplexing approach. By employing time-domain multiplexing, we generate a two-dimensional cluster state—a universal resource for large-scale quantum computation—and perform quantum operations in the time domain with cluster state. Additionally, our ongoing research focuses on the generation and measurement of broadband optical quantum entanglement through an optical parametric oscillator, which holds potential as a foundation for high-speed quantum computing surpassing limitations of existing systems. By further engineering the quantum entanglement, we have also theoretically formulated a practical teleportation-based architectures for quantum computation in time domain. These advancements form the groundwork for the development of practical optical quantum computation.
We developed a table-top multipass spectrograph with a 610-MHz resolution (corresponding to a resolving power of 450,000) and a throughput of 10%. The spectrograph was calibrated with a 4-GHz optical frequency comb (OFC) that did not require filtering cavities, which would hinder long-term operation. The OFC is centered at a wavelength of 1 μm, which makes it suitable for the investigation of M dwarf stars and the compact size of the OFC-calibrated spectrograph makes it suitable for use in small to mid-scale observatories.
In recent years, a calibration method for an astronomical spectrograph using an optical frequency comb (OFC) with a
repetition rate of more than ten GHz has been developed successfully [1-5]. But controlling filtering cavities that are
used for thinning out longitudinal modes precludes long term stability. The super-mode noise coming from the
fundamental repetition rate is an additional problem. We developed a laser-diode pumped Yb:Y2O3 ceramic oscillator,
which enabled the generation of 4-GHz (maximum repetition rate of 6.7 GHz) pulse trains directly with a spectrum
width of 7 nm (full-width half-maximum, FWHM), and controlled its optical frequency within a MHz level of accuracy
using a beat note between the 4-GHz laser and a 246-MHz Yb-fiber OFC. The optical frequency of the Yb-fiber OFC
was phase locked to a Rb clock frequency standard. Furthermore we also built a table-top multi-pass spectrograph with a
maximum frequency resolution of 600 MHz and a bandwidth of 1 nm using a large-size high-efficiency transmission
grating. The resolution could be changed by selecting the number of passes through the grating. This spectrograph could
resolve each longitudinal mode of our 4-GHz OFC clearly, and more than 10% throughput was obtained when the
resolution was set to 600 MHz. We believe that small and middle scale astronomical observatories could easily
implement such an OFC-calibrated spectrograph.
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