arXiv subjects

Ryoto Takai

Publications and source records attributed to Ryoto Takai.

8 recordsLinked to original sources

arXiv2026

Super-Heisenberg protocol for dark matter and high-frequency gravitational wave search

We propose a quantum-enhanced sensing scheme for the detection of wave-like dark matter and high-frequency gravitational waves using two-dimensional ion crystals in a Penning trap. The protocol employs spin-motion squeezed states to improve the signal-to-noise ratio and enable a super-Heisenberg scaling with respect to the number of ions over a broad parameter range. We analyze the sensitivity of the protocol to representative wave-like dark matter candidates, including the axion-like particle and the dark photon, as well as to high-frequency gravitational waves, taking into account the decoherence and dephasing of the ion spins. Our results indicate that two-dimensional ion crystals and this new protocol provide a promising platform for probing previously unexplored parameter space in searches for light dark matter and high-frequency gravitational waves.

hep-ph↗

arXiv2026

Coherent collective response in many-qubit systems for dark matter detection

We propose an array of Ramsey-type interferometers using $N$ superposition states, $(\vert 0 \rangle + \vert 1\rangle)^{\otimes N}$, as a sensor to detect wave-like dark matter. After exposure to the dark matter wave, which induces coherent qubit transitions, the signal is the imbalance between the numbers of 0 and 1 outcomes. The signal-to-noise ratio in this scheme is proportional to $N α^2$, where $α$ is the coupling of dark matter to the qubits, and thus the sensitivity to the coupling scales as $δα\sim 1 / \sqrt{N}$. For comparison, in the detection scheme based on the Rabi-type transition, $\vert 0 \rangle \to \vert 1\rangle$, this scaling is achieved only when $N$ highly entangled qubits are used. Since the Ramsey-type measurement does not require entangled states, one can consider much larger $N$ by simply placing a large number of qubits within the de Broglie wavelength of the dark matter. We demonstrate that, using trapped-ion qubits in linear Paul traps as the sensor, the projected sensitivity to the coupling matches or surpasses existing laboratory, astrophysical, and cosmological bounds for $N \gtrsim 10^6$-$10^8$. We also evaluate its sensitivity to high-frequency gravitational waves. Our general framework should, in principle, be useful for other quantum sensing platforms.

hep-ph↗

arXiv2026

Quantum sensing of high-frequency gravitational waves with ion crystals

A detection method for high-frequency gravitational waves using two-dimensional ion crystals is investigated. Gravitational waves can resonantly excite the drumhead modes of the ion crystal, particularly the parity-odd modes. In the optical dipole force protocol, entanglement between the drumhead modes and the collective spins transfers the excitation of the drumhead modes to the rotation of the total spin. Furthermore, gravitational wave detection beyond the standard quantum limit becomes possible as a squeezed spin state is generated through this entanglement. The sensitivity gets better with a larger ions crystals as well as a larger number of the ions. Future realization of large ion crystals can significantly improve the sensitivity to gravitational waves in the 10 kHz to 10 MHz region.

gr-qc↗

arXiv2026

Lepton number violating signals of a parity symmetric model at $μ$TRISTAN

The parity solution to the strong CP problem necessarily extends the Standard Model to include the SU$(2)_{\rm R}$ gauge sector and imposes restrictions on the structure of the Yukawa interactions. In this framework, one can consider an appealing structure of the neutrino sector in which the smallness of the neutrino masses is naturally explained, while lepton number symmetry is substantially violated at the TeV scale. Observation of distinctive lepton number violating signals at collider experiments can therefore be expected, since the rates are not suppressed by the small neutrino masses. We study the constraints from neutrinoless double beta decay and discuss the prospects for discovering new TeV-scale particles, such as the $W'$ boson of SU$(2)_{\rm R}$, via lepton number violating processes at a $μ^+ μ^+$ collider, $μ^+ μ^+ \to W^+ W'^+$. A $μ^+ μ^+$ collider with a center-of-mass energy of 10 TeV can probe the $W'$ boson mass up to about 10 TeV through on-shell production, and the reach can extend to 16 TeV by studying processes involving off-shell $W'$ boson.

hep-ph↗

arXiv2026

Probing high-frequency gravitational waves with entangled vibrational qubits in linear Paul traps

This work investigates the use of linear Paul traps as quantum sensors for detecting megahertz gravitational waves. Single-ion configurations exploit graviton-photon conversion in the presence of external magnetic fields, while two-ion systems use relative-motion excitations, which do not require magnets, to distinguish gravitational waves from axion dark matter. Furthermore, we show that entanglement of $N$ vibrational qubits enhances the signal probability by a factor of $N^2$, improving sensitivity beyond the standard quantum limit.

hep-ph↗

arXiv2025

Lepton flavor physics at $μ^+ μ^+$ colliders

We discuss sensitivities to lepton flavor violating (and conserving) interactions at future muon colliders, especially at $μ^+μ^+$ colliders. Compared with the searches for rare decays of $μ$ and $τ$, we find that the TeV-scale future colliders have better sensitivities depending on the pattern of hierarchy in the flavor mixings. As an example, we study the case with the type-II seesaw model, where the flavor mixing parameters have direct relation to the neutrino mass matrix. At a $μ^+ μ^+$ collider, the number of events of the $μ^+ μ^+ \to μ^+ τ^+$ process can be larger than $\mathcal{O}(100)$ with the center of mass energy $\sqrt s = 2$ TeV, and with an integrated luminosity ${\cal L} = 1$ ab$^{-1}$, while satisfying bounds from rare decays of $μ$ and $τ$. We discuss impacts of the overall mass scale of neutrinos as well as CP violating phases to the number of expected events.

hep-ph↗

arXiv2025

Higgs boson production at $μ^+ μ^+$ colliders

We study Higgs boson production at $μ^+ μ^+$ colliders at high energy. Since both initial-state particles are positively charged, there is no $W$ boson fusion at the leading order, as it requires a $W^+ W^-$ pair. However, we find that the cross section of the higher-order, $γ$- and $Z$-mediated $W$ boson fusion process is large at high center-of-mass energies $\sqrt s$, growing as $(\log s)^3$. This is in contrast to the $\log s$ behavior of the leading-order $W$ boson fusion. Thus, even though it is a higher-order process, the rate of Higgs boson production for 10 TeV energies at $μ^+ μ^+$ colliders with polarized beams can be as high as about half of the one at $μ^+ μ^-$ colliders, assuming the same integrated luminosity. To calculate the cross section of this process accurately, we carefully treat the collinear emission of the photon in the intermediate state. The thereby obtained large cross section furthermore shows the significance of Higgs production with an extra $W$ boson in the final state also at $μ^+ μ^-$ and $e^+ e^-$ colliders.

hep-ph↗

arXiv2024

Quantum entanglement of ions for light dark matter detection

A detection scheme is explored for light dark matter, such as axion dark matter or dark photon dark matter, using a Paul ion trap system. We first demonstrate that a qubit, constructed from the ground and first excited states of vibrational modes of ions in a Paul trap, can serve as an effective sensor for weak electric fields due to its resonant excitation. As a consequence, a Paul ion trap allows us to search for weak electric fields induced by light dark matter with masses around the neV range. Furthermore, we illustrate that an entangled qubit system involving $N$ ions can enhance the excitation rate by a factor of $N^2$. The sensitivities of the Paul ion trap system to axion-photon coupling and gauge kinetic mixing can reach previously unexplored parameter space.

hep-ph↗