Electron-on-Solid-Neon Qubit

Figure

Description

An electron-on-solid-neon qubit stores information in two quantized motional states of a single electron trapped above an ultraclean neon surface. Patterned electrodes create the lateral electrostatic trap; the electron remains in vacuum, bound vertically by its image potential and the surface barrier. Its electric dipole couples directly to a superconducting microwave resonator, giving a circuit-QED interface without embedding the carrier in a semiconductor crystal.

The 2022 demonstration achieved coherent microwave control and dispersive readout. This is a charge-like motional qubit, not yet an electron-spin qubit. The attraction is the exceptionally clean environment and large electric dipole; the cost is sensitivity to electric-field fluctuations, trap disorder, and electron loading.

Hamiltonian

Near a lateral trap minimum, the electron is approximately an anharmonic oscillator,

$H_e=\frac{{\hat{p}}_x^2}{2m_e}+V_{\mathrm{trap}}(\hat{x}),$

with the two lowest eigenstates selected as $|0⟩$ and $|1⟩$. Coupling to a microwave resonator is described in the rotating-wave approximation by

$\frac{H}{\hslash }={\omega }_r{a}^{†}a+\frac{{\omega }_q}{2}{\sigma }_z+g(a^{†}{\sigma }_{-}+a{\sigma }_{+}).$

The large motional dipole produces strong coupling $g$; detuning the qubit from the resonator enables dispersive readout.

Motivation

• Place a charge carrier in vacuum above an inert quantum solid rather than inside a noisy semiconductor interface.
• Combine fast electrical control with standard superconducting circuit-QED readout.
• Provide a route to floating-electron arrays and, eventually, spin storage with motional-state-mediated control.

Experimental Status

Zhou et al. demonstrated strong electron-photon coupling, microwave gates, and dispersive measurement of a single electron above solid neon in 2022. The reported motional-state lifetime was $T_1=15\mu \text{s}$ and phase coherence exceeded 200 ns. Multi-electron processors and high-fidelity two-qubit gates remain future work.

Key Metrics

Metric	Value	Notes	Fidelity reference
$T_1$	15 μs	Single-electron motional qubit	Zhou et al. 2022
$T_2$	>200 ns	Phase coherence in first device	Zhou et al. 2022
Readout	Dispersive	Superconducting microwave resonator	Zhou et al. 2022

Scaling Considerations

• Trap-to-trap frequency disorder and surface electric-field noise must be controlled across arrays.
• A scalable loading and shuttling protocol is needed for deterministic one-electron occupancy.
• The motional dipole is excellent for coupling but also exposes the qubit to charge noise.
• Spin-based storage could improve coherence, but that is a distinct, not-yet-demonstrated operating mode.

References

• X. Zhou et al., “Single electrons on solid neon as a solid-state qubit platform,” Nature 605, 46–50 (2022).

Linked Papers

• zhou-2022-solid-neon-electron-qubit

Evergreen context

• jaynes-cummings-in-circuits — electron-photon strong coupling and dispersive control use the same circuit-QED interaction layer as superconducting qubits.
• dispersive-readout-mechanism — explains how the motional state is inferred from a resonator shift.
• charge-noise-sweet-spot — the central comparison for a strongly electric-dipole-coupled motional qubit.

Related Entries

• semiconductor-charge-qubit — another electrically controlled charge-like encoding, but embedded in a semiconductor device.
• circuit-qed — shared microwave-control and readout architecture.