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arXiv:2501.02779 · Physical Review Applied

Image-charge detection of electrons on helium in an on-chip trapping device

Mikhail Belianchikov, Natália Morais, Denis Konstantinov

Published May 9, 2025• 5 citations
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Abstract

Electrons trapped on the surface of superfluid helium have been thought of as a useful resource for quantum computing. Such electrons show long coherence of their surface-bound (Rydberg) states combined with their easy electrostatic manipulation. Recent proposals have explored the possibility of coupling the spin state of an electron and the state of its quantized motion, with the promise of a highly scalable two-dimensional architecture for a quantum computer. However, despite recent progress in the detection of quantized lateral motion of electrons using a circuit-QED setup, manipulation of a small number of electrons and their quantum state detection remains a challenging problem. Here, we report on the detection of the Rydberg transition of electrons on superfluid helium in an on-chip microchannel device in which electrons are moved and trapped by a set of electrostatic gates. A highly sensitive image-charge detection system allows us to not only resolve the transition spectra of such electrons, but also perform the device characterization. The demonstrated sensitivity shows the feasibility of detecting the Rydberg transition of a single electron, which can open an alternate pathway for a nondestructive spin-state readout.

DOI
10.1103/physrevapplied.23.054026

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Electrons trapped on the surface of superfluid helium have been thought of as a useful resource for quantum computing. Such electrons show long coherence of their surface-bound (Rydberg) states combined with their easy electrostatic manipulation. Recent proposals have explored the possibility of coupling the spin state of an electron and the state of its quantized motion, with the promise of a highly scalable two-dimensional architecture for a quantum computer. However, despite recent progress in the detection of quantized lateral motion of electrons using a circuit-QED setup, manipulation of a small number of electrons and their quantum state detection remains a challenging problem. Here, we report on the detection of the Rydberg transition of electrons on superfluid helium in an on-chip microchannel device in which electrons are moved and trapped by a set of electrostatic gates. A highly sensitive image-charge detection system allows us to not only resolve the transition spectra of such electrons, but also perform the device characterization. The demonstrated sensitivity shows the feasibility of detecting the Rydberg transition of a single electron, which can open an alternate pathway for a nondestructive spin-state readout.
Abstract The image-charge detection provides a new direct method for the detection of the Rydberg transition of electrons trapped on the surface of liquid helium. The interest in this method is motivated by the possibility to accomplish the spin state readout for a single trapped electron, thus opening a new pathway towards using electron spins on liquid helium for quantum computing. Here, we report on the image-charge detection of the Rydberg transition in a many-electron system confined in an array of 20 μ m wide and 4 μ m deep channels filled with superfluid helium. Such detection is made possible because of a significant enhancement of the image-charge signal due to close proximity of trapped electrons to the electrodes embedded in the microchannel structure. The transition frequency of electrons in the range of 400–500 GHz is highly controllable by the dc bias voltages applied to the device and is in a good agreement with our calculations. This work demonstrates that microchannel structures provide a suitable platform for electron manipulation and their quantum state detection, with a feasibility of scaling the detection method to a single electron.
We propose a hybrid architecture in which an on-chip high finesse superconducting cavity is coupled to the lateral motion and spin state of a single electron trapped on the surface of superfluid helium. We estimate the motional coherence times to exceed 15 μs, while energy will be coherently exchanged with the cavity photons in less than 10 ns for charge states and faster than 1 μs for spin states, making the system attractive for quantum information processing and strong coupling cavity quantum electrodynamics experiments. The cavity is used for nondestructive readout and as a quantum bus mediating interactions between distant electrons or an electron and a superconducting qubit.
We propose to couple an on-chip high finesse superconducting cavity to the lateral-motion and spin state of a single electron trapped on the surface of superfluid helium. We estimate the motional coherence times to exceed 15 microseconds, while energy will be coherently exchanged with the cavity photons in less than 10 nanoseconds for charge states and faster than 1 microsecond for spin states, making the system attractive for quantum information processing and cavity quantum electrodynamics experiments. Strong interaction with cavity photons will provide the means for both nondestructive readout and coupling of distant electrons.
Quantum sensors that harness quantum coherence and entanglement are emerging as powerful tools in many fields, including particle physics, promising unprecedented sensitivity beyond classical detection methods. At the same time, electrons trapped on the surface of liquid helium have emerged as a promising quantum computing, and possibly sensing, platform owing to a nearly impurity-free environment and large predicted coherence times. In this context, single-electron confinement and control using microfabricated traps on helium has been experimentally demonstrated, highlighting the feasibility of scalable qubit architectures on this platform. In line with the DRD5 initiative at CERN, we propose here a sensor concept that uses an entangled pair of electron qubits on superfluid helium for particle physics experiments. We outline the motivation for such spatially and spin-entangled sensors, develop the theoretical formalism for two electrons and their spins and spatial degrees of freedom in a helium-based double-well trap (analogous to a double quantum dot in semiconductor systems), and discuss the potential advantages for detecting rare high-energy events with quantum-enhanced sensitivity. By exploiting quantum entanglement between the two trapped electrons, this sensor concept can surpass classical sensitivity limits, potentially enabling the detection of signals beyond the reach of classical detectors.
Electrons bound to the surface of liquid helium are an emerging quantum computing platform, offering the potential for highly mobile spin qubits that can be manipulated using CMOS-fabricated devices. Here, as a step toward realizing this technology, we demonstrate selective two-dimensional shuttling of electrons across a helium film condensed on the surface of a CMOS control chip. The electrons are moved in packets containing, on average, several tens down to single electrons. We perform CCD-style electron shuttling in any of 128 transport microchannels, each of which links electron storage zones and sensing zones in the 2D plane. Shuttling sequences can be repeated at least 109^99 times with no detectable electron loss. The device serves as a prototype quantum information processing platform that is readily scalable to control large monolithically integrated arrays of single electron spins.
Abstract Electrons trapped on the surface of liquid helium is an extremely clean system which holds promise for a scalable qubit platform. However, the superfluid surface is not free from fluctuations which might cause the decay and dephasing of the electron’s quantized states. Understanding and mitigating these fluctuations is essential for the advancement of electrons-on-helium qubit technology. Some work has been recently done to investigate surface oscillations due to the mechanical vibration of the cryostat using a superconducting coplanar waveguide resonator. In the present work, we focus on a sub-hertz frequency range and observe a strong effect of surface oscillations on the temporal dynamics of the Rydberg transition of electrons confined in a microchannel trapping device. We suggest possible origin of such oscillations and find a reasonable agreement between the corresponding estimation of the oscillation frequency and the observed result.