Multi-GHz光周波数コムによる精密分光研究

学位の種別: 課程博士審査委員会委員 : （主査）東京大学准教授 小林 洋平, 東京大学教授 志村 努, 東京大学特任教授 三尾 典克, 東京大学教授 香取 秀俊, 電気電信大学教授 美濃島 薫University of Tokyo(東京大学

Generation of optical Schr\"{o}dinger's cat states by generalized photon subtraction

We propose a high-rate generation method of optical Schr\"{o}dinger's cat states. Thus far, photon subtraction from squeezed vacuum states has been a standard method in cat-state generation, but its constraints on experimental parameters limit the generation rate. In this paper, we consider the state generation by photon number measurement in one mode of arbitrary two-mode Gaussian states, which is a generalization of conventional photon subtraction, and derive the conditions to generate high-fidelity and large-amplitude cat states. Our method relaxes the constraints on experimental parameters, allowing us to optimize them and attain a high generation rate. Supposing realistic experimental conditions, the generation rate of cat states with large amplitudes ($|\alpha| \ge 2)$ can exceed megacounts per second, about $10^3$ to $10^6$ times better than typical rates of conventional photon subtraction. This rate would be improved further by the progress of related technologies. Ability to generate non-Gaussian states at a high rate is important in quantum computing using optical continuous variables, where scalable computing platforms have been demonstrated but preparation of non-Gaussian states of light remains as a challenging task. Our proposal reduces the difficulty of the state preparation and open a way for practical applications in quantum optics.Comment: 8 pages, 5 figure

Ultra-low phase noise microwave generation with a free-running monolithic femtosecond laser

Phase noise performance of photonic microwave systems, such as optical frequency division (OFD), can surpass state-of-the-art electronic oscillators by several orders of magnitude. However, high-finesse cavities and active stabilization requirements in OFD systems make them complicated and potentially unfit for field deployment. Ultra-low noise mode-locked monolithic lasers offer a viable alternative for a compact and simple photonic microwave system. Here we present a free-running monolithic laser-based 8 GHz microwave generation with ultra-low phase noise performance comparable to laboratory OFD systems. The measured noise performance reached &minus;130 dBc/Hz at 100 Hz, &ndash; 150 dBc/Hz at 1 kHz, and &ndash;167 dBc/Hz at 10 kHz offsets from the 8-GHz carrier. We also report a sub-Poissonian noise floor of &minus;179 dBc/Hz above 30 kHz (timing noise floor of 32 zs Hz&minus;1/2), which is &sim;12 dB below the noise floor of time-invariant shot noise. In addition to the low phase noise, the system is compact, with a power consumption of less than 9 W, and offers excellent potential for mobile or space-borne applications.</p

X-Band photonic microwaves with phase noise below-180 dBc/Hz using a free-running monolithic comb

Free-running mode-locked monolithic optical frequency combs offer a compact and simple alternative to complicated optical frequency division schemes. Ultra-low free-running noise performance of these oscillators removes the necessity of external phase stabilization, making the microwave systems uncomplicated and compact with lower power consumption while liberating the sidebands of the carrier from servo bumps typically present around hundreds of kilohertz offsets. Here we present a free-running monolithic laser-based 8 GHz photonic microwaves generation and characterization with a cryogenically cooled power splitter to demonstrate a state-of-the-art phase noise floor of less than &minus;180 dBc/Hz below 1 MHz offset from the carrier. &nbsp;</p

Gaussian breeding for encoding a qubit in propagating light

Practical quantum computing requires robust encoding of logical qubits in physical systems to protect fragile quantum information. Currently, the lack of scalability limits the logical encoding in most physical systems, and thus the high scalability of propagating light can be a game changer for realizing a practical quantum computer. However, propagating light also has a drawback: the difficulty of logical encoding due to weak nonlinearity. Here, we propose Gaussian breeding that encodes arbitrary Gottesman-Kitaev-Preskill (GKP) qubits in propagating light. The key idea is the efficient and iterable generation of quantum superpositions by photon detectors, which is the most widely used nonlinear element in quantum propagating light. This formulation makes it possible to systematically create the desired qubits with minimal resources. Our simulations show that GKP qubits above a fault-tolerant threshold, including ``magic states'', can be generated with a high success probability and with a high fidelity exceeding 0.99. This result fills an important missing piece toward practical quantum computing.Comment: 19 pages, 2 figure

Quantum detector tomography of superconducting nanostrip photon-number-resolving detector

Superconducting nanostrip photon detectors have been used as single photon detectors, which can discriminate only photons' presence or absence. It has recently been found that they can discriminate the number of photons by analyzing the output signal waveform, and they are expected to be used in various fields, especially in optical quantum information processing. Here, we improve the photon-number-resolving performance for light with a high-average photon number by pattern matching of the output signal waveform. Furthermore, we estimate the positive-operator-valued measure of the detector by a quantum detector tomography. The result shows that the device has photon-number-resolving performance up to five photons without any multiplexing or arraying, indicating that it is useful as a photon-number-resolving detector.Comment: 11 pages, 5 figure

Structure and dynamics of room temperature ionic liquids with bromide anion: Results from 81Br NMR spectroscopy

We report the results of a comprehensive 81Br NMR spectroscopic study of the structure and dynamics of two room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium bromide ([C4mim]Br) and 1-butyl-2,3-dimethylimidazolium bromide ([C4C1mim]Br), in both liquid and crystalline states. NMR parameters in the gas phase are also simulated for stable ion pairs using quantum chemical calculations. The combination of 81Br spin-lattice and spin-spin relaxation measurements in the motionally narrowed region of the stable liquid state provides information on the correlation time of the translational motion of the cation. 81Br quadrupolar coupling constants (CQ) of the two RTILs were estimated to be 6.22 and 6.52 MHz in the crystalline state which were reduced by nearly 50% in the liquid state, although in the gas phase, the values are higher and span the range of 7-53 MHz depending on ion pair structure. The CQ can be correlated with the distance between the cation-anion pairs in all the three states. The 81Br CQ values of the bromide anion in the liquid state indicate the presence of some structural order in these RTILs, the degree of which decreases with increasing temperature. On the other hand, the ionicity of these RTILs is estimated from the combined knowledge of the isotropic chemical shift and the appropriate mean energy of the excited state. [C4C1mim]Br has higher ionicity than [C4mim]Br in the gas phase, while the situation is reverse for the liquid and the crystalline states. Copyright © 2015 John Wiley & Sons, Ltd

Single-shot single-mode optical two-parameter displacement estimation beyond classical limit

Uncertainty principle prohibits the precise measurement of both components of displacement parameters in phase space. We have theoretically shown that this limit can be beaten using single-photon states, in a single-shot and single-mode setting [F. Hanamura et al., Phys. Rev. A 104, 062601 (2021)]. In this paper, we validate this by experimentally beating the classical limit. In optics, this is the first experiment to estimate both parameters of displacement using non-Gaussian states. This result is related to many important applications, such as quantum error correction.Comment: 5 pages, 4 figure