Abstract Interest is growing in the development of quantum sensing based on the principles of quantum mechanics, such as discrete energy levels, quantum superposition, and quantum entanglement. Superconducting flux qubits are quantum two-level systems whose energy is sensitive to a magnetic field. Therefore, they can be used as high-sensitivity magnetic field sensors that detect the magnetization of a spin ensemble. Since the magnetization depends on temperature and the magnetic field, the temperature can be determined by measuring the magnetization using the flux qubit. In this study, we demonstrated highly sensitive temperature sensing with high spatial resolution as an application of a magnetic field sensor using the quantum coherence of a superconducting flux qubit. By using a superconducting flux qubit to detect the temperature dependence of the polarization ratio of electron spins in nano-diamond particles, we succeeded in measuring the temperature with a sensitivity of 1.3 µKµ Hz − 1 at T = 9.1 mK in the submicrometer range.Abstract Interest is growing in the development of quantum sensing based on the principles of quantum mechanics, such as discrete energy levels, quantum superposition, and quantum entanglement. Superconducting flux qubits are quantum two-level systems whose energy is sensitive to a magnetic field. Therefore, they can be used as high-sensitivity magnetic field sensors that detect the magnetization of a spin ensemble. Since the magnetization depends on temperature and the magnetic field, the temperature can be determined by measuring the magnetization using the flux qubit. In this study, we demonstrated highly sensitive temperature sensing with high spatial resolution as an application of a magnetic field sensor using the quantum coherence of a superconducting flux qubit. By using a superconducting flux qubit to detect the temperature dependence of the polarization ratio of electron spins in nano-diamond particles, we succeeded in measuring the temperature with a sensitivity of 1.3 µKµ Hz − 1 at T = 9.1 mK in the submicrometer range.

New Journal of PhysicsJan 1, 20236 citations

On the Quantum Measurement of Superconducting Flux Qubits

Thomas Picot

Sep 22, 20100 citations

Macroscopic Quantum Phenomena and Coherence in Superconducting Networks

Carlo Giovannella, M. Tinkham

Jan 1, 199690 citations

Fast partial decoherence of a superconducting flux qubit in a spin bath

Jacek Dziarmaga

The superconducting flux qubit has two quantum states with opposite currents which generate different magnetic fields. Environment of nuclear spins can find out the magnetic field after a decoherence time ${\ensuremath{\tau}}_{0}$ inversely proportional to the magnetic field and the square root of the number of spins. When the Hamiltonian of the qubit drives fast coherent Rabi oscillations between the states with opposite current, then the magnetic field is flipped at a constant rate $\ensuremath{\omega}$ and the decoherence time $\ensuremath{\tau}=\ensuremath{\omega}{\ensuremath{\tau}}_{0}^{2}$ is much longer than ${\ensuremath{\tau}}_{0}$. However, on closer inspection decoherence actually takes place on two time scales. The long time $\ensuremath{\tau}$ is a time of full decoherence but a part of quantum coherence is lost already after the much shorter time $\ensuremath{\pi}∕\ensuremath{\omega}$. This fast partial decoherence biases coherent flux oscillations towards the initial flux direction and it can affect performance of the superconducting devices as qubits.The superconducting flux qubit has two quantum states with opposite currents which generate different magnetic fields. Environment of nuclear spins can find out the magnetic field after a decoherence time ${\ensuremath{\tau}}_{0}$ inversely proportional to the magnetic field and the square root of the number of spins. When the Hamiltonian of the qubit drives fast coherent Rabi oscillations between the states with opposite current, then the magnetic field is flipped at a constant rate $\ensuremath{\omega}$ and the decoherence time $\ensuremath{\tau}=\ensuremath{\omega}{\ensuremath{\tau}}_{0}^{2}$ is much longer than ${\ensuremath{\tau}}_{0}$. However, on closer inspection decoherence actually takes place on two time scales. The long time $\ensuremath{\tau}$ is a time of full decoherence but a part of quantum coherence is lost already after the much shorter time $\ensuremath{\pi}∕\ensuremath{\omega}$. This fast partial decoherence biases coherent flux oscillations towards the initial flux direction and it can affect performance of the superconducting devices as qubits.

arXiv:cond-mat/0410161Physical Review BFeb 25, 20051 citation

Dynamically suppressing cavity dephasing induced by frequency fluctuations of a coupled nonlinear mode

Yunwei Lu, Xinyuan You, Ziwen Huang +3 more

High-coherence superconducting cavities offer a promising platform for quantum information, with long coherence times and negligible intrinsic dephasing. However, cavity control generally relies on nonlinear Josephson elements whose frequency fluctuations are inherited by the cavity as dephasing, potentially limiting control fidelities and eroding the noise bias used in error-correction protocols. Here, we introduce Stark-Assisted Flux-noise Evasion (SAFE), a hardware-efficient protocol that protects the cavity from inherited dephasing using only a weak off-resonant microwave drive applied to the nonlinear element. As a concrete setup, we analyze a 3D superconducting cavity dispersively coupled to a flux-tunable transmon (FTT) subject to $1/f$ flux noise. Analytical predictions are confirmed by Monte Carlo simulations with realistic parameters, which show that SAFE can extend the cavity dephasing time by more than an order of magnitude while keeping residual drive-induced decoherence subdominant.High-coherence superconducting cavities offer a promising platform for quantum information, with long coherence times and negligible intrinsic dephasing. However, cavity control generally relies on nonlinear Josephson elements whose frequency fluctuations are inherited by the cavity as dephasing, potentially limiting control fidelities and eroding the noise bias used in error-correction protocols. Here, we introduce Stark-Assisted Flux-noise Evasion (SAFE), a hardware-efficient protocol that protects the cavity from inherited dephasing using only a weak off-resonant microwave drive applied to the nonlinear element. As a concrete setup, we analyze a 3D superconducting cavity dispersively coupled to a flux-tunable transmon (FTT) subject to $1/f$ flux noise. Analytical predictions are confirmed by Monte Carlo simulations with realistic parameters, which show that SAFE can extend the cavity dephasing time by more than an order of magnitude while keeping residual drive-induced decoherence subdominant.

quant-pharXiv:2608.04494Aug 6, 20260 citations

1/f

flux noise. Analytical predictions are confirmed by Monte Carlo simulations with realistic parameters, which show that SAFE can extend the cavity dephasing time by more than an order of magnitude while keeping residual drive-induced decoherence subdominant.