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Experimental setup for a Rydberg atom-mechanical oscillator hybrid system

Cedric Wind

Published Apr 10, 2026• 0 citations
OpenAlex

Abstract

Hybrid quantum systems provide a promising route toward combining the complementary strengths of distinct physical platforms for quantum information processing. In this context, highly excited Rydberg atoms are particularly attractive due to their strong electric dipole moments, long lifetimes, and compatibility with both optical and microwave frequency regimes. Mechanical resonators, on the other hand, offer long coherence times and the ability to store quantum information in macroscopic degrees of freedom. In this thesis, the development of a novel hybrid platform interfacing ultracold Rydberg atoms with high-overtone bulk acoustic wave resonators (HBARs) in a cryogenic environment is presented. The core components of the experimental apparatus have been designed, assembled, and characterized, including a room-temperature realization featuring the complete cold-atom preparation chain. A first-generation superconducting atom chip for trapping ultracold atoms in a cryogenic environment has been designed and fabricated, establishing the foundation for future experiments under cryogenic conditions. The full experimental realization of the hybrid system, including the integration of the mechanical resonator, was delayed by the delivery of a custom-built cryostat. Nevertheless, the preparation of the cryogenic experiment has been completed, enabling rapid progress toward first experiments once cryogenic operation becomes available. At an operating temperature of 4 K, thermal phonon occupation of HBAR modes is significantly reduced compared to room temperature but remains above the quantum ground state, motivating the development of active cooling strategies. Complementing the experimental work, the feasibility of cooling a mechanical mode toward its quantum mechanical ground state using a cloud of Rydberg atoms is investigated theoretically. In this approach, Rydberg atoms act as a dissipative resource that extracts phononic excitations from the mechanical resonator and removes them via radiative decay. Furthermore, the potential of Rydberg atom-mediated interactions to generate entanglement between spatially separated mechanical oscillators is analyzed. Together, these results establish a foundation for future experimental investigations of Rydberg atom–mechanical oscillator hybrid systems.

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Hybrid quantum systems provide a promising route toward combining the complementary strengths of distinct physical platforms for quantum information processing. In this context, highly excited Rydberg atoms are particularly attractive due to their strong electric dipole moments, long lifetimes, and compatibility with both optical and microwave frequency regimes. Mechanical resonators, on the other hand, offer long coherence times and the ability to store quantum information in macroscopic degrees of freedom. In this thesis, the development of a novel hybrid platform interfacing ultracold Rydberg atoms with high-overtone bulk acoustic wave resonators (HBARs) in a cryogenic environment is presented. The core components of the experimental apparatus have been designed, assembled, and characterized, including a room-temperature realization featuring the complete cold-atom preparation chain. A first-generation superconducting atom chip for trapping ultracold atoms in a cryogenic environment has been designed and fabricated, establishing the foundation for future experiments under cryogenic conditions. The full experimental realization of the hybrid system, including the integration of the mechanical resonator, was delayed by the delivery of a custom-built cryostat. Nevertheless, the preparation of the cryogenic experiment has been completed, enabling rapid progress toward first experiments once cryogenic operation becomes available. At an operating temperature of 4 K, thermal phonon occupation of HBAR modes is significantly reduced compared to room temperature but remains above the quantum ground state, motivating the development of active cooling strategies. Complementing the experimental work, the feasibility of cooling a mechanical mode toward its quantum mechanical ground state using a cloud of Rydberg atoms is investigated theoretically. In this approach, Rydberg atoms act as a dissipative resource that extracts phononic excitations from the mechanical resonator and removes them via radiative decay. Furthermore, the potential of Rydberg atom-mediated interactions to generate entanglement between spatially separated mechanical oscillators is analyzed. Together, these results establish a foundation for future experimental investigations of Rydberg atom–mechanical oscillator hybrid systems.
In modern quantum technology, different quantum systems have properties that make them effective for some tasks and less beneficial for others. Integrating these systems together into a single quantum hybrid system, exploiting the advantages of each systems strengths while suppressing their disadvantages, can advance the total performance. On-chip quantum hybrid systems coupled to an ensemble of ultracold atoms show a great potential for advancing quantum technology, because they combine the long coherence time of the atomic ensemble with access to conventional read-out techniques provided by the chip. This thesis presents an apparatus that we have built to carry out experiments with coupling ultracold 87Rb gases to various systems, including nanomechanics and optical cavities. The apparatus operates at ultra-high vacuum conditions, required for experiments with ultracold gases, and its design allows us to easily and quickly switch between different on-chip devices to perform and study quantum hybridization with ultracold gases. Such versatility is provided by separating the region where the ultracold gas is created from the location of the chip, and implementing a system which can optically transfer the atoms between these two regions. In this work we also describe atom cooling techniques used in this experiment, including magneto-optical trapping, sub-Doppler cooling in optical molasses and evaporative cooling. These methods have demonstrated cooling to temperatures below 100 uK. We also discuss a setup for optimal optical-dipole transport. Finally, we theoretically consider magnetic coupling between atoms and nanomechanical oscillators and propose using the Landau-Zener transitions as a method for reducing or measuring mechanical temperature of the resonators, and to create quantum entanglement between multiple devices.
A promising route to novel quantum technologies are hybrid quantum systems, which combine the advantages of several individual quantum systems. We have realized a hybrid atomic-mechanical experiment consisting of a Si 3 N 4 membrane oscillator cryogenically precooled to 500 mK and optically coupled to a cloud of laser cooled 87 Rb atoms. Here, we demonstrate active feedback cooling of the oscillator to a minimum mode occupation of corresponding to a mode temperature of T min ≈ 200 μ K. Furthermore, we characterize in detail the coupling of the membrane to the atoms by means of sympathetic cooling. By simultaneously applying both cooling methods we demonstrate the possibility of preparing the oscillator near the motional ground state while it is coupled to the atoms. Realistic modifications of our setup will enable the creation of a ground state hybrid quantum system, which opens the door for coherent quantum state transfer, teleportation and entanglement as well as quantum enhanced sensing applications.
Hybrid quantum systems involving cold atoms and microwave resonators can enable cavity-mediated infinite-range interactions between atomic spin systems and realize atomic quantum memories and transducers for microwave-to-optical conversion. To achieve strong coupling of atoms to on-chip microwave resonators, it was suggested to use atomic Rydberg states with strong electric-dipole transitions. Here we report on the experimental realization of coherent coupling of a Rydberg transition of ultracold atoms, trapped on an integrated superconducting atom chip, to the microwave field of an on-chip coplanar waveguide resonator. Close to the chip surface, stray electric fields lead to inhomogeneous Rydberg level shifts, which would hinder coherent interactions of atoms in a cloud with the Rydberg excitation lasers and the microwave cavity field. We, however, use optical excitation of a Rydberg state of atoms in a narrow layer with nearly constant electric field, which allows for resonant coupling of the atoms to the cavity microwave field on an appropriate Rydberg transition. We also achieve state-selective detection of the energetically close Rydberg states. We then observe and characterize cavity-driven Rabi oscillations between a pair of atomic Rydberg states. The residual damping of the oscillations is dominated by the spread of Rabi frequencies of atoms in different positions of the resonant cavity mode, as revealed by our model. Despite the technical challenges, our studies demonstrate the feasibility of coherent-state manipulation of Rydberg atoms interacting with superconducting circuits, paving the way for realization of capable hybrid quantum systems.
This thesis intends to give a concise yet meaningful overview about the progress in the physical realization of quantum information processing using hybrid systems of ultracold atoms and superconducting microwave resonators, describing our own theoretical and experimental contributions to advancing. Ultracold atoms in their ground states are well-isolated quantum systems offering long coherence times, and therefore are prime candidates for quantum memory applications. Their performance is limited by their sensitivity on external magnetic-field noises and inhomogeneous Zeeman shifts inherently present in magnetic traps. We have developed an efficient method to eliminate the magnetic-field dependence of the differential Zeeman shift between the magnetically trappable clock-states up to second order around an arbitrarily chosen offset field, hence rendering atom-based quantum memory insensitive to magnetic noises. We describe two protocols to mediate long-range interactions between Rydberg atoms using a thermally populated microwave cavity, realizing universal 2-bit quantum gates. This is of great practical interest, since in existing hybrid atom-superconducting resonator experiments the attainable temperature is not low enough to reach the vacuum state of the cavity mode. The first method relies on active mode cooling using an auxiliary reservoir of atoms. The second method makes use of a destructive quantum interference between different excitation paths, making the scheme insensitive to the actual photon state of the cavity. We also report on a new laboratory for optical lattice clocks that we have established in parallel with this work. We present a novel concept for continuously operated atomic clocks, along with the steps we have taken towards its experimental realization.
In this thesis theoretical studies of hybrid quantum systems composed of solid-state superconducting microwave resonators, mechanical oscillators, and gas-phase Rydberg atoms are described. The thesis begins with an overview of the current state of the field of hybrid quantum in- formation processing. An introduction to the physics of Rydberg atoms and the preparation processes of circular Rydberg states follows, including a review of the associated literature. Three main new research results are then presented. These include (1) numerical studies of static electric dipole interactions in strongly polarized gases of Rydberg atoms. The understanding and characterization of these interactions is essential to maximize the quantum-state preparation procedures required for the hybrid systems studied in the thesis; (2) analytical and numerical studies of quantum-state preparation and cooling in coplanar superconducting microwave resonators using beams of atoms in circular Rydberg states; and (3) studies of coupled Rydberg-atom—mechanical-oscillator systems. The results presented in each of these areas are of interest for hybrid quantum information processing and quantum computation, and optical-to- microwave photon conversion for quantum communication.
Mechanical resonators are a promising way for interfacing qubits in order to realize hybrid quantum systems that offer great possibilities for applications. Mechanical systems can have very long energy lifetimes, and they can be further interfaced to other systems. Moreover, integration of a mechanical oscillator with qubits creates a potential platform for the exploration of quantum physics in macroscopic mechanical degrees of freedom. The utilization of high overtone bulk acoustic resonators coupled to superconducting qubits is an intriguing platform towards these goals. These resonators exhibit a combination of high-frequency and high-quality factors. They can reach their quantum ground state at dilution refrigeration temperatures and they can be strongly coupled to superconducting qubits via their piezoelectric effect. In this paper, we demonstrate our system where bulk acoustic phonons of a high overtone resonator are coupled to a transmon qubit in a planar circuit architecture. We show that the bulk acoustic phonons are interacting with the qubit in a simple design architecture at the quantum level, representing further progress towards the quantum control of mechanical motion.