arXiv subjects

Kosuke Shibata

Publications and source records attributed to Kosuke Shibata.

At least 19 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

Toward the theory on local cohomologies at the ideals given by simplicial posets

For a simplicial poset $P$, Stanley assigned the face ring $A_P$, which is the quotient of the polynomial ring $S:=K[t_x \mid x \in P \setminus \{\widehat{0} \}]$ by the ideal $I_P$. This is a generalization of Stanley-Reisner rings, but $S$ and $A_P$ are not standard graded in this case, and $I_P$ is not a monomial ideal. To establish the foundation of the theory on local cohomology $H_{I_p}^i(S)$ and its injective resolution, we give an explicit description of the graded injective envelope ${}^*\! E_S(S/\mathfrak{p}_x)$, where $\mathfrak{p}_x$is the prime ideal associated with $x \in P$, and analyze their behavior in the graded dualizing complex.

math.AC↗

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↗

arXiv2025

Dispersive measurement of spin shot noise in a Bose--Einstein condensate

We report dispersive spin shot noise measurement of a Bose--Einstein condensate (BEC). While dispersive probing has been used for quantum spin noise measurement of thermal and cold gases for decades, confirmative measurement of spin shot noise, i.e.,\ the linear dependence of the spin variance on the number of atoms in a BEC has been lacking. Here, we demonstrate precise spin noise measurement of a BEC of rubidium atoms at the spin shot noise level by polarization rotation using a two-color probe at optimal detunings, with power balance stabilization to suppress probe-induced excess spin noise. This work opens the possibility for the unexplored study of quantum spin fluctuations in multi-component or spinor BECs and offers an approach to improve spin measurement precision, which is relevant to atomic spin-based sensors.

cond-mat.quant-gas↗

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↗

arXiv2022

Multi-state interferometric measurement of nonlinear AC Stark shift

We demonstrate measurement of quadratic AC Stark shifts between Zeeman sublevels in an $^{87}$Rb Bose--Einstein condensate using a multi-state atomic interferometer. The interferometer can detect a quadratic shift without being affected by relatively large state-independent shifts, thereby improving the measurement precision. We measure quadratic shifts in the total spin $F = 2$ state due to the light being near-resonant to the D$_1$ line. The agreement between the measured and theoretical detuning dependences of the quadratic shifts confirms the validity of the measurement. We also present results on the suppression of nonlinear spin evolution using near-resonant dual-color light pulses with opposite quadratic shifts.

physics.atom-ph↗

arXiv2022

Elementary construction of the minimal free resolution of the Specht ideal of shape $(n-d,d)$

Let $K$ be a field with ${\rm char}(K)=0$. For a partition $\lambda$ of $n \in {\mathbb N}$, let $I^{\rm Sp}_\lambda$ be the ideal of $R=K[x_1,\ldots,x_n]$ generated by all Specht polynomials of shape $\lambda$. These ideals have been studied from several points of view (and under several names). Using advanced tools of the representation theory, Berkesch Zamaere et al [BGS]. constructed a minimal free resolution of $I^{\rm Sp}_{(n-d,d)}$ except differential maps. The present paper constructs the differential maps, and also gives an elementary proof of the result of [BGS].

math.AC↗

arXiv2021

Quantum lock-in detection of a vector light shift

We demonstrate detection of a vector light shift (VLS) using the quantum lock-in method. The method offers precise and accurate VLS measurement without being affected by real magnetic field fluctuations. We detect a VLS on a Bose--Einstein condensate (BEC) of $^{87}$Rb atoms caused by an optical trap beam with a resolution less than 1 Hz. We also demonstrate elimination of a VLS by controlling the beam polarization to realize a long coherence time of a transversally polarized $F$ = 2 BEC. Quantum lock-in VLS detection should find wide application, including the study of spinor BECs, electric-dipole moment searches, and precise magnetometry.

cond-mat.quant-gas↗

arXiv2020

Elementary construction of minimal free resolutions of the Specht ideals of shapes $(n-2,2)$ and $(d,d,1)$

For a partition $\lambda$ of $n \in \mathbb{N}$, let $I^{\rm Sp}_\lambda$ be the ideal of $R=K[x_1,\ldots,x_n]$ generated by all Specht polynomials of shape $\lambda$. We assume that ${\rm char}(K)=0$. Then $R/I^{\rm Sp}_{(n-2,2)}$ is Gorenstein, and $R/I^{\rm Sp}_{(d,d,1)}$ is a Cohen-Macaulay ring with a linear free resolution. In this paper, we construct minimal free resolutions of these rings. Berkesch Zamaere, Griffeth, and Sam had already studied minimal free resolutions of $R/I^{\rm Sp}_{(n-d,d)}$, which are also Cohen-Macaulay, using heighly advanced technique of the representation theory. However we only use the basic theory of Specht modules, and explicitly describe the differential maps.

math.AC↗

arXiv2020

Sensitive BEC magnetometry with optimized probing

An improved spatial magnetometer using a spinor Bose-Einstein condensate of $^{87}$Rb atoms is realized utilizing newly developed two-polarization phase contrast imaging. The optical shot noise is suppressed by carefully choosing the probe parameters. We attain a dc-magnetic field sensitivity of 7.7 ${\rm pT/\sqrt{Hz}}$ over a measurement area of 28 ${\rm μm^{2}}$. The attained sensitivity per unit area is superior to that for other modern low-frequency magnetometers with micrometer-order spatial resolution. This result is a promising step for realizing quantum-enhanced magnetometry surpassing classical methods.

physics.atom-ph↗

arXiv2020

Cohen-Macaulay edge-weighted edge ideals of very well-covered graphs

We characterize unmixed and Cohen-Macaulay edge-weighted edge ideals of very well-covered graphs. We also provide examples of oriented graphs which have unmixed and non-Cohen-Macaulay vertex-weighted edge ideals, while the edge ideal of their underlying graph is Cohen-Macaulay. This disproves a conjecture posed by Pitones, Reyes and Toledo.

math.AC↗

arXiv2020

Regularity of Cohen-Macaulay Specht ideals

For a partition $\lambda$ of $n \in {\mathbb N}$, let $I^{\rm Sp}_\lambda$ be the ideal of $R=K[x_1,\ldots,x_n]$ generated by all Specht polynomials of shape $\lambda$. In the previous paper, the second author showed that if $R/I^{\rm Sp}_\lambda$ is Cohen-Macaulay, then $\lambda$ is either $(n-d,1,\ldots,1),(n-d,d)$, or $(d,d,1)$, and the converse is true if ${\rm char}(K)=0$. In this paper, we compute the Hilbert series of $R/I^{\rm Sp}_\lambda$ for $\lambda=(n-d,d)$ or $(d,d,1)$. Hence, we get the Castelnuovo-Mumford regularity of $R/I^{\rm Sp}_\lambda$, when it is Cohen-Macaulay. In particular, $I^{\rm Sp}_{(d,d,1)}$ has a $(d+2)$-linear resolution in the Cohen-Macaulay case.

math.AC↗

arXiv2019

Alexander duality for the alternative polarizations of strongly stable ideals

We will define the Alexander duality for strongly stable ideals. More precisely, for a strongly stable ideal $I \subset \Bbbk[x_1, \ldots, x_n]$ with ${\rm deg}(\mathsf{m}) \le d$ for all $\mathsf{m} \in G(I)$, its dual $I^* \subset \Bbbk[y_1, \ldots, y_d]$ is a strongly stable ideal with ${\rm deg}(\mathsf{m}) \le n$ for all $\mathsf{m} \in G(I^*)$. This duality has been constructed by Fl$ø$ystad et al. in a different manner, so we emphasis applications here. For example, we will describe the Hilbert serieses of the local cohomologies $H_\mathfrak{m}^i(S/I)$ using the irreducible decomposition of $I$ (through the Betti numbers of $I^*$).

math.AC↗

arXiv2019

Compensation of gravity on cold atoms by a linear optical potential

We demonstrate gravity compensation for an ultracold gas of $^{87}$Rb atoms with a time-averaged optical potential. The position of a far-off-resonance beam is temporally modulated with an acousto-optic deflector to efficiently produce a potential with a linear gradient independent of the atomic magnetic sublevels. We realize compensation of the gravity sag and preparation of a degenerate gas in a trap with weak vertical confinement. Optical gravity compensation will provide the opportunity to perform experiments under microgravity in a laboratory and broaden the scope of cold atom research.

physics.atom-ph↗

arXiv2019

Faraday patterns generated by Rabi oscillation in a binary Bose-Einstein condensate

The interaction between atoms in a two-component Bose-Einstein condensate (BEC) is effectively modulated by the Rabi oscillation. This periodic modulation of the effective interaction is shown to generate Faraday patterns through parametric resonance. We show that there are multiple resonances arising from the density and spin waves in a two-component BEC, and investigate the interplay between the Faraday-pattern formation and the phase separation.

cond-mat.quant-gas↗

arXiv2018

Loading of atoms into an optical trap with high initial phase-space density

We report a method for loading cold atoms into an optical trap with high initial phase-space density (PSD). When the trap beam is overlapped with atoms in optical molasses of optimized parameters including large cooling beam detuning compared with conventional detuning used for a magneto-optical trap (MOT), more than $3 \times 10^6$ rubidium atoms with an initial temperature less than 20 $μ$K are loaded into a single beam trap. The obtained maximum initial PSD is estimated to be $1.1 \times 10^{-3}$, which is one or two orders of magnitude greater than that achieved with the conventional loading into an optical trap from atoms in a MOT. The proposed method is promising for creating a quantum gas with a large number of atoms in a short evaporation time.

cond-mat.quant-gas↗

arXiv2018

Interaction modulation in a long-lived Bose-Einstein condensate by rf coupling

We demonstrate modulation of the effective interaction between the magnetic sublevels of the hyperfine spin $F=1$ in a $^{87}$Rb Bose-Einstein condensate by Rabi coupling with radio-frequency (rf) field. The use of the $F=1$ manifold enables us to observe the long-term evolution of the system owing to the absence of inelastic collisional losses. We observe that the evolution of the density distribution reflects the change in the effective interaction between atoms due to rf coupling. We also realize a miscibility-to-immiscibility transition in the magnetic sublevels of $m = \pm 1$ by quenching the rf field. Rf-induced interaction modulation in long-lived states as demonstrated here will facilitate the study of out-of-equilibrium quantum systems.

physics.atom-ph↗