Electron-spin resonance is a useful tool to investigate properties of materials in magnetic fields where high spin polarization of target electron spins is required in order to obtain high sensitivity. However, the smaller the magnetic fields becomes, the more difficult it is to obtain high polarization by thermalization. Here, we propose to employ a superconducting flux qubit (FQ) to polarize electron spins actively. We have to overcome a large energy difference between the FQ and electron spins for efficient energy transfer among them. For this purpose, we adopt a spin-lock technique on the FQ where the Rabi frequency associated with the spin-locking can match the resonance (Larmor) one of the electron spins. We find that adding dephasing on the spins is beneficial to obtain high polarization of them, because otherwise the electron spins are trapped in dark states that cannot be coupled with the FQ. We show that our scheme can achieve high polarization of electron spins in realistic experimental conditions.Electron-spin resonance is a useful tool to investigate properties of materials in magnetic fields where high spin polarization of target electron spins is required in order to obtain high sensitivity. However, the smaller the magnetic fields becomes, the more difficult it is to obtain high polarization by thermalization. Here, we propose to employ a superconducting flux qubit (FQ) to polarize electron spins actively. We have to overcome a large energy difference between the FQ and electron spins for efficient energy transfer among them. For this purpose, we adopt a spin-lock technique on the FQ where the Rabi frequency associated with the spin-locking can match the resonance (Larmor) one of the electron spins. We find that adding dephasing on the spins is beneficial to obtain high polarization of them, because otherwise the electron spins are trapped in dark states that cannot be coupled with the FQ. We show that our scheme can achieve high polarization of electron spins in realistic experimental conditions.

arXiv:2108.02463Physical Review AJan 28, 20221 citation

A New Spin on Superconductivity

Marric Stephens

PhysicsAug 19, 20260 citations

New Trends in Superconductivity

James F. Annett, S. P. Kruchinin

Springer eBooksJan 1, 200240 citations

High-fidelity quantum memory with floating electrons coupled to superconducting circuits

Ji-kun Xie, Rong-teng Cao, Ya-long Ren +3 more

Hybridizing different degrees of freedom or physical platforms potentially offers various advantages in building scalable quantum architectures. We study the hybrid quantum system of a single electron trapped on a solid neon surface, where the motional states of an electron interact with microwave photons in an on-chip superconducting cavity. By applying a nonuniform magnetic field with a gradient along the vibrational axis, the spin-orbit coupling of the electron's spin degree of freedom and its lateral motion can be engineered. We show that the electron's spin states with ultralong coherence time as a quantum memory can be explored to store the quantum information of a superconducting qubit. As an extension, we also propose to implement high-quality quantum state transfer between the spin states of two electrons trapped in spatially separated superconducting cavities. The present work may have practical applications for realizing floating-electron-based hybrid quantum computation.Hybridizing different degrees of freedom or physical platforms potentially offers various advantages in building scalable quantum architectures. We study the hybrid quantum system of a single electron trapped on a solid neon surface, where the motional states of an electron interact with microwave photons in an on-chip superconducting cavity. By applying a nonuniform magnetic field with a gradient along the vibrational axis, the spin-orbit coupling of the electron's spin degree of freedom and its lateral motion can be engineered. We show that the electron's spin states with ultralong coherence time as a quantum memory can be explored to store the quantum information of a superconducting qubit. As an extension, we also propose to implement high-quality quantum state transfer between the spin states of two electrons trapped in spatially separated superconducting cavities. The present work may have practical applications for realizing floating-electron-based hybrid quantum computation.

Physical Review ANov 18, 20241 citation

Vibration-induced field fluctuations in a superconducting magnet

J. Britton, Justin Bohnet, Brian C. Sawyer +3 more

Superconducting magnets enable precise control of nuclear and electron spins, and are used in experiments that explore biological and condensed-matter systems, and fundamental atomic particles. In high-precision applications, a common view is that slow $(<1\phantom{\rule{4.pt}{0ex}}\mathrm{Hz})$ drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10--200 Hz) that limits the coherence time of $^{9}\text{Be}^{+}$ electron-spin qubits in the $4.46\ensuremath{-}\mathrm{T}$ field of a superconducting magnet. We measure a spin-echo ${T}_{2}$ coherence time of $\ensuremath{\sim}6\phantom{\rule{0.28em}{0ex}}\text{ms}$ for the $^{9}\text{Be}^{+}$ electron-spin resonance at $124\phantom{\rule{0.28em}{0ex}}\text{GHz}$ , limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved ${T}_{2}$ to $\ensuremath{\sim}50$ ms.Superconducting magnets enable precise control of nuclear and electron spins, and are used in experiments that explore biological and condensed-matter systems, and fundamental atomic particles. In high-precision applications, a common view is that slow $(<1\phantom{\rule{4.pt}{0ex}}\mathrm{Hz})$ drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10--200 Hz) that limits the coherence time of $^{9}\text{Be}^{+}$ electron-spin qubits in the $4.46\ensuremath{-}\mathrm{T}$ field of a superconducting magnet. We measure a spin-echo ${T}_{2}$ coherence time of $\ensuremath{\sim}6\phantom{\rule{0.28em}{0ex}}\text{ms}$ for the $^{9}\text{Be}^{+}$ electron-spin resonance at $124\phantom{\rule{0.28em}{0ex}}\text{GHz}$, limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved ${T}_{2}$ to $\ensuremath{\sim}50$ ms.

arXiv:1512.00801Physical Review AJun 27, 201620 citations

Tunable Superconductivity

ScienceJul 7, 20050 citations

(<1\phantom{\rule{4.pt}{0ex}}\mathrm{Hz})

drift of the homogeneous magnetic-field limits control and measurement precision. We report on previously undocumented higher-frequency field noise (10--200 Hz) that limits the coherence time of

^{9}\text{Be}^{+}

electron-spin qubits in the $4.46\ensuremath{-}\mathrm{T}$ field of a superconducting magnet. We measure a spin-echo

{T}_{2}

coherence time of $\ensuremath{\sim}6\phantom{\rule{0.28em}{0ex}}\text{ms}$ for the

^{9}\text{Be}^{+}

electron-spin resonance at

124\phantom{\rule{0.28em}{0ex}}\text{GHz}

, limited by part-per-billion fractional fluctuations in the magnet's homogeneous field. Vibration isolation of the magnet improved

{T}_{2}

to $\ensuremath{\sim}50$ ms.