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Coherence protection of a silicon hole spin qubit with phase-modulated microwave driving
Authors:
Sayyid I. Ibad,
Yusuke Sato,
Takuma Kuno,
Itaru Yanagi,
Toshiyuki Mine,
Ryuta Tsuchiya,
Digh Hisamoto,
Hiroyuki Mizuno,
Raisei Mizokuchi,
Jun Yoneda,
Tetsuo Kodera
Abstract:
Hole spins in silicon quantum dots are a promising platform for quantum computing due to their strong intrinsic spin-orbit coupling (SOC), which enables fast, all-electrical control. However, this coupling also increases their susceptibility to charge noise, thereby limiting coherence times. Moreover, holes in silicon are also affected by hyperfine interactions with residual nuclear spins in the s…
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Hole spins in silicon quantum dots are a promising platform for quantum computing due to their strong intrinsic spin-orbit coupling (SOC), which enables fast, all-electrical control. However, this coupling also increases their susceptibility to charge noise, thereby limiting coherence times. Moreover, holes in silicon are also affected by hyperfine interactions with residual nuclear spins in the silicon substrate, introducing a non-negligible source of low-frequency noise. Here, we implement a phase-modulated concatenated continuous driving (CCD) technique for hole spin qubits to suppress low-frequency noise through microwave phase modulation. This approach stabilizes Rabi oscillations and extends the oscillation decay time compared to the conventional method. Furthermore, by defining a qubit in the CCD frame, we achieve coherent control while simultaneously protecting the qubit from noise, confirming coherence protection during gate operations. These results demonstrate a viable route toward noise-robust hole spin qubits.
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Submitted 20 August, 2026;
originally announced August 2026.
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Valley enhanced Rabi frequency in n-type planar Silicon-MOS quantum dot
Authors:
Xunyao Luo,
Xander Peetroons,
Tsung-Yeh Yang,
Ruben M. Otxoa,
Normann Mertig,
Sofie Beyne,
Julien Jussot,
Yosuke Shimura,
Clement Godfrin,
Bart Raes,
Roy Li,
Roger Loo,
Sylvain Baudot,
Stefan Kubicek,
Shuchi Kaushik,
Danny Wan,
Kristiaan De Greve,
Takuma Kuno,
Takeru Utsugi,
Noriyuki Lee,
Itaru Yanagi,
Toshiyuki Mine,
Satoshi Muraoka,
Hideo Arimoto,
Shinichi Saito
, et al. (5 additional authors not shown)
Abstract:
Electron spin resonance spectroscopy (ESR) of a single electron in planar Si-MOS quantum dot is reported in the vicinity of a valley level anti-crossing. A number of one and two-photon resonances are observed due to mixing of magnetic spin-flip and electric valley-flip transitions. This allows the reconstruction of the energy-level diagram of a four state system with two valley and two spin states…
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Electron spin resonance spectroscopy (ESR) of a single electron in planar Si-MOS quantum dot is reported in the vicinity of a valley level anti-crossing. A number of one and two-photon resonances are observed due to mixing of magnetic spin-flip and electric valley-flip transitions. This allows the reconstruction of the energy-level diagram of a four state system with two valley and two spin states. Near the anti-crossing, an enhancement of the Rabi frequency is observed. This is attributed to an electric-dipole transition activated by admixing of the upper energy level due to inter-valley spin coupling. The electric-dipole transition may be driven via capacitive coupling between the ESR antenna, and the confinement gate. To characterize spin-valley coupling responsible for the enhancement, we measure the anisotropy of the g-factor difference between the two valley states, the mean g-factor and the inter-valley spin coupling for both in and out-of-plane magnetic fields. The inter-valley spin coupling is strongly modulated by the direction of the B-field, and is strongest for out-of-plane B-field, consistent with an in-plane spin-valley field. In principle, this strong Electric dipole spin resonance (EDSR) effect could be utilized for fast all-electrical spin control in small-scale devices.
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Submitted 24 April, 2026;
originally announced April 2026.
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High Fidelity Qubit Control in a Natural Si-MOS Quantum Dot using a 300 mm Silicon on Insulator Wafer
Authors:
Xander Peetroons,
Xunyao Luo,
Tsung-Yeh Yang,
Normann Mertig,
Sofie Beyne,
Julien Jussot,
Yosuke Shimura,
Clement Godfrin,
Bart Raes,
Ruoyu Li,
Roger Loo,
Sylvain Baudot,
Stefan Kubicek,
Shuchi Kaushik,
Danny Wan,
Takeru Utsugi,
Takuma Kuno,
Noriyuki Lee,
Itaru Yanagi,
Toshiyuki Mine,
Satoshi Muraoka,
Shinichi Saito,
Digh Hisamoto,
Ryuta Tsuchiya,
Hiroyuki Mizuno
, et al. (4 additional authors not shown)
Abstract:
We demonstrate high-fidelity single qubit control in a natural Si-MOS quantum dot fabricated in an industrial 300 mm wafer process on a silicon on insulator (SOI) wafer using electron spin resonance. A relatively high optimal Rabi frequency of 5 MHz is achieved, dynamically decoupling the electron spin from its 29-Si environment. Tracking the qubit frequency reduces the impact of low frequency noi…
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We demonstrate high-fidelity single qubit control in a natural Si-MOS quantum dot fabricated in an industrial 300 mm wafer process on a silicon on insulator (SOI) wafer using electron spin resonance. A relatively high optimal Rabi frequency of 5 MHz is achieved, dynamically decoupling the electron spin from its 29-Si environment. Tracking the qubit frequency reduces the impact of low frequency noise in the qubit frequency and improves the $T^{Rabi}$ from 7 to 11 $μ$s at a Rabi frequency of 5 MHz, resulting in Q-factors exceeding 50. Randomized benchmarking returns an average single gate control fidelity of 99.5 $\pm$ 0.3%. As a result of pulse-area calibration, this fidelity is limited by the Rabi Q-factor. These results show that a fast Rabi frequency, low charge noise, and a feedback protocol enable high fidelity in these Si-MOS devices, despite the low-frequency magnetic noise.
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Submitted 4 December, 2025;
originally announced December 2025.
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Robust spin-qubit control in a natural Si-MOS quantum dot using phase modulation
Authors:
Takuma Kuno,
Takeru Utsugi,
Andrew J. Ramsay,
Normann Mertig,
Noriyuki Lee,
Itaru Yanagi,
Toshiyuki Mine,
Nobuhiro Kusuno,
Raisei Mizokuchi,
Takashi Nakajima,
Shinichi Saito,
Digh Hisamoto,
Ryuta Tsuchiya,
Jun Yoneda,
Tetsuo Kodera,
Hiroyuki Mizuno
Abstract:
Silicon quantum dots are one of the most promising candidates for practical quantum computers because of their scalability and compatibility with the well-established complementary metal-oxide-semiconductor technology. However, the coherence time is limited in industry-standard natural silicon because of the $^{29}$Si isotopes, which have non-zero nuclear spin. Here, we protect an isotopically nat…
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Silicon quantum dots are one of the most promising candidates for practical quantum computers because of their scalability and compatibility with the well-established complementary metal-oxide-semiconductor technology. However, the coherence time is limited in industry-standard natural silicon because of the $^{29}$Si isotopes, which have non-zero nuclear spin. Here, we protect an isotopically natural silicon metal-oxide-semiconductor (Si-MOS) quantum dot spin qubit from environmental noise via electron spin resonance with a phase-modulated microwave (MW) drive. This concatenated continuous drive (CCD) method extends the decay time of Rabi oscillations from 1.2 $\mathrm{μs}$ to over 200 $\mathrm{μs}$. Furthermore, we define a protected qubit basis and propose robust gate operations. We find the coherence time measured by Ramsey sequence is improved from 143 ns to 40.7 $μ$s compared to that of the bare spin qubit. The single qubit gate fidelity measured with randomized benchmarking is improved from 95% to 99%, underscoring the effectiveness of the CCD method. The method shows promise for improving control fidelity of noisy qubits, overcoming the qubit variability for global control, and maintaining qubit coherence while idling.
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Submitted 22 January, 2026; v1 submitted 25 March, 2025;
originally announced March 2025.
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Thermal circuit model for silicon quantum-dot array structures
Authors:
Takeru Utsugi,
Nobuhiro Kusuno,
Takuma Kuno,
Noriyuki Lee,
Itaru Yanagi,
Toshiyuki Mine,
Shinichi Saito,
Digh Hisamoto,
Ryuta Tsuchiya,
Hiroyuki Mizuno
Abstract:
Temperature rise of qubits due to heating is a critical issue in large-scale quantum computers based on quantum-dot (QD) arrays. This leads to shorter coherence times, induced readout errors, and increased charge noise. Here, we propose a simple thermal circuit model to describe the heating effect on silicon QD array structures. Noting that the QD array is a periodic structure, we represent it as…
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Temperature rise of qubits due to heating is a critical issue in large-scale quantum computers based on quantum-dot (QD) arrays. This leads to shorter coherence times, induced readout errors, and increased charge noise. Here, we propose a simple thermal circuit model to describe the heating effect on silicon QD array structures. Noting that the QD array is a periodic structure, we represent it as a thermal distributed-element circuit, forming a thermal transmission line. We validate this model by measuring the electron temperature in a QD array device using Coulomb blockade thermometry, finding that the model effectively reproduces experimental results. This simple and scalable model can be used to develop the thermal design of large-scale silicon-based quantum computers.
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Submitted 26 August, 2025; v1 submitted 19 December, 2024;
originally announced December 2024.
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Single electron routing in a silicon quantum-dot array
Authors:
Takeru Utsugi,
Takuma Kuno,
Noriyuki Lee,
Ryuta Tsuchiya,
Toshiyuki Mine,
Digh Hisamoto,
Shinichi Saito,
Hiroyuki Mizuno
Abstract:
The ability to transport single electrons on a quantum dot array dramatically increases the freedom in designing quantum computation schemes that can be implemented on solid-state devices. So far, however, routing schemes to precisely control the transport paths of single electrons have yet to be established. Here, we propose a silicon single-electron router that transports pumped electrons along…
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The ability to transport single electrons on a quantum dot array dramatically increases the freedom in designing quantum computation schemes that can be implemented on solid-state devices. So far, however, routing schemes to precisely control the transport paths of single electrons have yet to be established. Here, we propose a silicon single-electron router that transports pumped electrons along the desired route on the branches of a T-shaped quantum dot array by inputting a synchronous phase-controlled signal to multiple gates. Notably, we show that it is possible to achieve a routing accuracy above 99\% by boosting the accuracy of the electron-transport timing with an assist gate in front of the branching paths. We also evaluated the minimum error rate of routing by the model of electron transport based on the Wigner representation in an energy-time space. The results suggest new possibilities for fast and accurate transport of single electrons on the two-dimensional quantum dot arrays.
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Submitted 19 January, 2025; v1 submitted 9 August, 2023;
originally announced August 2023.
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Site-resolved imaging of single atoms with a Faraday quantum gas microscope
Authors:
Ryuta Yamamoto,
Jun Kobayashi,
Kohei Kato,
Takuma Kuno,
Yuto Sakura,
Yoshiro Takahashi
Abstract:
We successfully demonstrate a quantum gas microscopy using the Faraday effect which has an inherently non-destructive nature. The observed Faraday rotation angle reaches 3.0(2) degrees for a single atom. We reveal the non-destructive feature of this Faraday imaging method by comparing the detuning dependence of the Faraday signal strength with that of the photon scattering rate. We determine the a…
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We successfully demonstrate a quantum gas microscopy using the Faraday effect which has an inherently non-destructive nature. The observed Faraday rotation angle reaches 3.0(2) degrees for a single atom. We reveal the non-destructive feature of this Faraday imaging method by comparing the detuning dependence of the Faraday signal strength with that of the photon scattering rate. We determine the atom distribution with deconvolution analysis. We also demonstrate the absorption and the dark field Faraday imaging, and reveal the different shapes of the point spread functions for these methods, which are fully explained by theoretical analysis. Our result is an important first step towards an ultimate quantum non-demolition site-resolved imaging and furthermore opens up the possibilities for quantum feedback control of a quantum many-body system with a single-site resolution.
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Submitted 24 July, 2016;
originally announced July 2016.
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An ytterbium quantum gas microscope with narrow-line laser cooling
Authors:
Ryuta Yamamoto,
Jun Kobayashi,
Takuma Kuno,
Kohei Kato,
Yoshiro Takahashi
Abstract:
We demonstrate site-resolved imaging of individual bosonic $^{174}\mathrm{Yb}$ atoms in a Hubbard-regime two-dimensional optical lattice with a short lattice constant of 266 nm. To suppress the heating by probe light with the $^1S_0$-$^1P_1$ transition of the wavelength $λ$ = 399 nm for high-resolution imaging and preserve atoms at the same lattice sites during the fluorescence imaging, we simulta…
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We demonstrate site-resolved imaging of individual bosonic $^{174}\mathrm{Yb}$ atoms in a Hubbard-regime two-dimensional optical lattice with a short lattice constant of 266 nm. To suppress the heating by probe light with the $^1S_0$-$^1P_1$ transition of the wavelength $λ$ = 399 nm for high-resolution imaging and preserve atoms at the same lattice sites during the fluorescence imaging, we simultaneously cool atoms by additionally applying narrow-line optical molasses with the $^1S_0$-$^3P_1$ transition of the wavelength $λ$ = 556 nm. We achieve a low temperature of $T = 7.4(1.3)\ μ\mathrm{K}$, corresponding to a mean oscillation quantum number along the horizontal axes of 0.22(4) during imaging process. We detect on average 200 fluorescence photons from a single atom within 400 ms exposure time, and estimate the detection fidelity of 87(2)%. The realization of a quantum gas microscope with enough fidelity for Yb atoms in a Hubbard-regime optical lattice opens up the possibilities for studying various kinds of quantum many-body systems such as Bose and Fermi gases, and their mixtures, and also long-range-interacting systems such as Rydberg states.
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Submitted 10 September, 2015;
originally announced September 2015.