arXiv subjects

Tetsushi Takano

Publications and source records attributed to Tetsushi Takano.

18 recordsLinked to original sources

arXiv2026

Minimally Destructive Fast Imaging of Single Atoms in an Optical Tweezer Array with Coherent Excitation

Ultracold neutral atoms in an optical lattice and an optical tweezer array offer highly-controllable quantum many-body systems, utilized for various quantum science and technology such as quantum computing, quantum metrology, and quantum simulation. By combining high-fidelity imaging of individual atoms, one can further enhance the capability of such experimental platforms as quantum gas microscopes, tweezer clocks, and tweezer-array-based quantum computers. In this work, we propose a minimally destructive single-atom imaging by deterministic coherent excitation of atoms with alternately applied pi-pulses from counter-propagating directions, mitigating the fundamental heating effect associated with the stochastic absorption process. Using ytterbium-174 atoms trapped in an optical tweezer array, we experimentally demonstrate fast and low-loss single-atom imaging with a discrimination fidelity of 99.89(5) % and a survival probability of 98.80(44) % in 17.6 microseconds. Importantly, our scheme exhibits the lower heating rate, about half of that of the former scheme utilizing the incoherent excitation. This fast and minimally destructive imaging scheme is beneficial for relaxing the requirement on the trap depth, thereby enabling scalable atom imaging across a wide range of quantum science platforms.

physics.atom-ph↗

arXiv2026

Orders-of-magnitude improvement in precision spectroscopy of an inner-shell orbital clock transition in neutral ytterbium

An inner-shell orbital clock transition $^1S_0 \leftrightarrow 4f^{13}5d6s^2 \: (J=2)$ in neutral ytterbium atoms has attracted much attention as a new optical frequency standard as well as a highly sensitive probe for several new physics phenomena, such as ultralight dark matter, violation of local Lorentz invariance, and a new Yukawa potential between electrons and neutrons. Here, we demonstrate almost two-orders-of-magnitude improvement in precision spectroscopy over the previous reports on this transition, achieved by trapping atoms in a three-dimensional magic-wavelength optical lattice. In particular, we successfully observe the coherent Rabi oscillation, the relaxation dynamics of the excited state and the interorbital Feshbach resonance. To highlight the high precision of our spectroscopy, we carry out precise isotope shift measurements between five stable bosonic isotopes well below 10 Hz uncertainties, successfully setting bounds for a hypothetical boson mediating a force between electrons and neutrons. These results open up the way for various new physics search experiments and a wide range of applications to quantum science with this clock transition.

physics.atom-ph↗

arXiv2026

Spin-Cat Qubit with Biased Noise in an Optical Tweezer Array

Bias-tailored quantum error correcting codes (QECCs) offer a higher error threshold than standard QECCs and have the potential to achieve lower logical errors with less space overhead. The spin-cat qubit, encoded in a large nuclear spin-$F$ system, is a promising candidate for bias-tailored QECCs. Yet its feasibility is hindered by the difficulty of performing fast covariant SU(2) rotation with arbitrary rotation angles for nuclear spins and by a lack of noise characterization for gate operations in neutral atom platforms. Here we demonstrate single-qubit controls of ${}^{173}\mathrm{Yb}$ spin-cat qubits with nuclear spin $I=5/2$ in an optical tweezer array. We implement a covariant SU(2) rotation and non-linear rotations by optical beams and achieve an averaged single-Clifford gate fidelity of $0.961_{-5}^{+5}$. The measurement of the coherence time and spin relaxation time shows that the idling error becomes increasingly biased toward dephasing errors as the magnitude of the encoded sublevel $|m_F|$ increases. Furthermore, we benchmark the noise bias of rank-preserving gates on spin-cat qubits, demonstrating a finite bias of $18_{-11}^{+132}$, in contrast to the case of the two-level system in ${}^{171}\mathrm{Yb}$, which shows no bias within the experimental uncertainty. Our work demonstrates the feasibility of spin-cat qubits for realizing bias-tailored QECCs, paving the way for achieving hardware-efficient quantum error correction.

quant-ph↗

arXiv2026

Excluding Hypothetical Light Boson Interpretation of Yb King Plot Nonlinearity with the ${}^1S_0 \leftrightarrow {}^3P_2$ Isotope Shift Measurement

We present precision spectroscopy and isotope shift measurement of the ${}^1S_0 \leftrightarrow {}^3P_2$ clock transition in neutral ytterbium ($\mathrm{Yb}$) atoms. By revealing a magic wavelength at $905.4(2)$ nm, we successfully achieve the atomic spectrum narrower than $100$ Hz. The interleaved clock operation between isotopes allows us to determine isotope shifts of four bosonic isotope pairs at Hz-level uncertainties, which is combined with those of other four ultra-narrow transitions in $\mathrm{Yb}$ and $\mathrm{Yb}^+$ to construct the King plot. Importantly, the new isotope shift data reported in this work is a key to exclude the possibility of attributing the observed nonlinearity of the three-dimensional King plot solely to the new physics, while the previous works rely on the other terrestrial bound set by the neutron scattering and $(g-2)_e$ measurements. This work paves the way for the effective use of precision isotope shift data in the King plot analysis and stimulates further measurements in $\mathrm{Yb}$ and other elements.

physics.atom-ph↗

arXiv2025

Plane-selective manipulations of nuclear spin qubits in a three-dimensional optical tweezer array

One of the central challenges for a practical fault-tolerant quantum computer is scalability. A three-dimensional structure of optical tweezer arrays offers the potential for scaling up neutral atom processors. However, coherent local operations, essential for quantum error correction, have yet to be explored for this platform. Here, we demonstrate plane-by-plane initialization of nuclear spin qubits of ${}^{171}\mathrm{Yb}$ atoms in a three-dimensional atom array and plane-dependent coherent temporal evolution of qubits, as well as plane-selective qubit manipulation by exploiting the plane-selective excitation of the atoms from the ${}^1S_0$ to the ${}^3P_2$ state. This plane-selective manipulation technique paves the way for quantum computing and quantum simulation in three-dimensional multilayer architectures.

quant-ph↗

arXiv2024

Development of a high-power ultraviolet laser system and observation of fast coherent Rydberg excitation of ytterbium

We present the development of a high-power ultraviolet laser system operating at a wavelength of 325 nm for Rydberg excitation from the ${}^3\mathrm{P}_2$ state of ytterbium. Utilizing a two-stage frequency doubling scheme, we achieved an output power exceeding 800 mW. The system effectively suppresses frequency noise in the MHz range, which is critical for achieving high Rydberg excitation fidelity, through the use of a filtering cavity. Using this system, we demonstrated coherent excitation of the $(6s71s){}^3\mathrm{S}_1$ Rydberg state with a Rabi frequency of 2.13(3) MHz. Combined with our successful manipulations on the ${}^1\mathrm{S}_0-{}^3\mathrm{P}_2$ transition, this work represents a foundational step toward achieving high-fidelity Rydberg excitation, enabling advancements in quantum simulation and computing with neutral atom arrays.

physics.atom-ph↗

arXiv2024

A hybrid atom tweezer array of nuclear spin and optical clock qubits

While data qubits with a long coherence time are essential for the storage of quantum information, ancilla qubits are pivotal in quantum error correction (QEC) for fault-tolerant quantum computing. The recent development of optical tweezer arrays, such as the preparation of large-scale qubit arrays and high-fidelity gate operations, offers the potential for realizing QEC protocols, and one of the important next challenges is to control and detect ancilla qubits while minimizing atom loss and crosstalk. Here, we present the realization of a hybrid system consisting of a dual-isotope ytterbium (Yb) atom array, in which we can utilize a nuclear spin qubit of fermionic ${}^{171}\mathrm{Yb}$ as a data qubit and an optical clock qubit of bosonic ${}^{174}\mathrm{Yb}$ as an ancilla qubit with a capacity of non-destructive qubit readout. We evaluate the crosstalk between qubits regarding the impact on the coherence of the nuclear spin qubits from the imaging light for ${}^{174}\mathrm{Yb}$. The Hahn-echo sequence with a 399 nm probe and 556 nm cooling beams for ${}^{174}\mathrm{Yb}$, we observe 99.1(1.8) % coherence retained under 20 ms exposure, yielding an imaging fidelity of 0.9992 and a survival probability of 0.988. The Ramsey sequence with a 556 nm probe beam shows negligible influence on the coherence, suggesting the potential future improvement of low cross-talk measurements. This result highlights the potential of the hybrid-Yb atom array for ancilla-qubit-based QEC protocols.

quant-ph↗

arXiv2023

Observation of an Inner-Shell Orbital Clock Transition in Neutral Ytterbium Atoms

We observe a weakly allowed optical transition of atomic ytterbium from the ground state to the metastable state $4f^{13}5d6s^2 \: (J=2)$ for all five bosonic and two fermionic isotopes with resolved Zeeman and hyperfine structures. This inner-shell orbital transition has been proposed as a new frequency standard as well as a quantum sensor for new physics. We find magic wavelengths through the measurement of the scalar and tensor polarizabilities and reveal that the measured trap lifetime in a three-dimensional optical lattice is 1.9(1) s, which is crucial for precision measurements. We also determine the $g$ factor by an interleaved measurement, consistent with our relativistic atomic calculation. This work opens the possibility of an optical lattice clock with improved stability and accuracy as well as novel approaches for physics beyond the standard model.

physics.atom-ph↗

arXiv2022

Gallium-nitride-based interference-filter-stabilized external cavity diode laser with a surface-activated-bonded output coupler

We report on an interference-filter-stabilized external cavity diode laser using a gallium-nitride-based violet laser diode. Surface-activated-bonded glass substrates were employed as cat's eye output couplers in order to suppress power degradation due to optical damage. From the results of a long-term frequency-stabilization test, mode-hop-free operation for about one week was demonstrated. After a continuous operation of about three weeks, the power degradation was less than 10$\%$. The results show the potential of such interference-filter-stabilized external cavity diode lasers for practical and portable quantum technologies such as atomic clocks or atomic interferometers.

physics.atom-ph↗

arXiv2022

Observation of non-linearity of generalized King plot in the search for new boson

We measure isotope shifts for neutral Yb isotopes on an ultranarrow optical clock transition $^{1}\text{S}_{0}-^{3}\text{P}_{0}$ with an accuracy of a few Hz. The part-per-billion precise measurement was possible by loading the ultracold atoms into a three-dimensional magic-wavelength optical lattice and alternately interrogating the isotope pairs, thus minimizing the effects due to the optical lattice light-shift and inter-atomic interaction as well as the drifts of a clock laser frequency and a magnetic field. The determined isotope shifts, combined with one of the recently reported isotope-shift measurements of Yb$^+$ on two optical transitions, allow us to construct the King plots. Extremely large nonlinearity with the corresponding $χ^2$ on the order of $10^4$ is revealed, and is not explained by a quadratic field shift. We further carry out the generalized King plot for three optical transitions so that we can eliminate the contribution arising from a higher-order effect within the Standard Model which might explain the observed nonlinearity of King plots for two transitions. Our analysis of the generalized King plot shows a deviation from linearity at the 3$σ$ level, indicating that there exist at least two higher order contributions in the measured isotope shifts. Then, under the reasonable assumption to attribute them to higher-order field shifts within the Standard Model, we obtain the upper bound of the product of the couplings for a new boson mediating a force between electrons, and neutrons $|y_ey_n|/(\hbar c)< 1\times10^{-10}$ for the mass less than 1 keV with the 95% confidence level is derived, providing an important step towards probing new physics via isotope-shift spectroscopy.

physics.atom-ph↗

arXiv2021

10 W injection-locked single-frequency continuous-wave titanium:sapphire laser

High-power tunable lasers with good longitudinal and transverse modes are fundamental tools for exploring quantum physics. Here we report a high-power continuous-wave injection-locked titanium:sapphire laser with a low-loss cavity configuration, where only a laser crystal was installed in the laser cavity. Although the transverse mode was affected by a thermal lens formed in the laser crystal, the focal length of the thermal lens could be shifted via the temperature of the laser crystal holder or the pump power. As a result, we found a condition that 10 W single-frequency oscillation with a good transverse mode and a slope efficiency of 51% were achieved.

physics.optics↗

arXiv2017

Precise determination of the isotope shift of ${}^{88}$Sr - ${}^{87}$Sr optical lattice clock by sharing perturbations

We report on the isotope shift between ${}^{88}$Sr and ${}^{87}$Sr on the ${}^1S_0 - {}^3P_0$ clock transitions. The interleaved operation of an optical lattice clock with two isotopes allows the canceling out of common perturbations, such as the quadratic Zeeman shift, the clock-light shift, and the blackbody radiation shift. The isotope shift is determined to be 62 188 134.004(10) Hz, where the major uncertainty is introduced by the collisional shift that is distinct for each isotope. Our result allows us to determine the frequency of $^{88}$Sr-$^{87}$Sr optical lattice clocks with a fractional uncertainty of $2\times 10^{-17}$. The scheme is generally applicable for measuring the isotope shift with significantly reduced uncertainty.

physics.atom-ph↗

arXiv2016

Real-time geopotentiometry with synchronously linked optical lattice clocks

According to the Einstein's theory of relativity, the passage of time changes in a gravitational field. On earth, raising a clock by one centimetre increases its tick rate by 1.1 parts in 10$^{18}$, enabling optical clocks to perform precision geodesy. Here, we demonstrate geopotentiometry by determining the height difference of master and slave clocks separated by 15 km with uncertainty of 5 cm. The subharmonic of the master clock is delivered through a telecom fibre to phase-lock and synchronously interrogate the slave clock. This protocol rejects laser noise in the comparison of two clocks, which improves the stability of measuring the gravitational red shift. Such phase-coherently operated clocks facilitate proposals for linking clocks and interferometers. Over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be $1,652.9(5.9)\times 10^{-18}$, or a height difference of 1,516(5) cm, consistent with an independent measurement by levelling and gravimetry. Our system is as a building block of an internet of clocks, consisting of a master and a number of slave clocks, which will provide "quantum benchmarks" that are height references with dynamic response.

physics.atom-ph↗

arXiv2015

Frequency ratios of Sr, Yb and Hg based optical lattice clocks and their applications

This article describes the recent progress of optical lattice clocks with neutral strontium ($^{87}$Sr), ytterbium ($^{171}$Yb) and mercury ($^{199}$Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on a Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an optical frequency comb, the ratios of the clock frequencies are determined with uncertainties smaller than possible through absolute frequency measurements. Finally, we describe a synchronous frequency comparison between two Sr-based remote clocks over a distance of 15 km between RIKEN and the University of Tokyo, as a step towards relativistic geodesy.

physics.atom-ph↗

arXiv2014

Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom-atom and atom-wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturisation. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kKagome-lattice hollow-core photonic crystal fibre (HC-PCF) are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom-atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the $^1 S_0-{}^3P_1$ (m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibresHC-PCFs improve the optical depth while preserving atomic coherence time.

physics.atom-ph↗

arXiv2011

Direct Comparison of Distant Optical Lattice Clocks at the $10^{-16}$ Uncertainty

Fiber-based remote comparison of $^{87}$Sr lattice clocks in 24 km distant laboratories is demonstrated. The instability of the comparison reaches $5\times10^{-16}$ over an averaging time of 1000 s, which is two orders of magnitude shorter than that of conventional satellite links and is limited by the instabilities of the optical clocks. By correcting the systematic shifts that are predominated by the differential gravitational redshift, the residual fractional difference is found to be $(1.0\pm7.3)\times10^{-16}$, confirming the coincidence between the two clocks. The accurate and speedy comparison of distant optical clocks paves the way for a future optical redefinition of the second.

physics.atom-ph↗

arXiv2009

Manipulation of Non-classical Atomic Spin States

We report successful manipulation of non-classical atomic spin states. We generate squeezed spin states by a spin quantum nondemolition measurement, and apply an off-resonant circularly-polarized light pulse to the atoms. By changing the pulse duration, we have clearly observed a rotation of anisotropic quantum noise distribution in good contrast with the case of manipulation of a coherent spin state where the quantum noise distribution is always isotropic. This is an important step for quantum state tomography, quantum swapping, and precision spectroscopic measurement.

quant-ph↗

arXiv2009

Measurement schemes for the spin quadratures on an ensemble of atoms

We consider how to measure collective spin states of an atomic ensemble based on the recent multi-pass approaches for quantum interface between light and atoms. We find that a scheme with two passages of a light pulse through the atomic ensemble is efficient to implement the homodyne tomography of the spin state. Thereby, we propose to utilize optical pulses as a phase-shifter that rotates the quadrature of the spins. This method substantially simplifies the geometry of experimental schemes.

quant-ph↗