Session G53: Hybrid Quantum Systems

All-Optical Single Shot Readout of a Superconducting Qubit

The rapid development of superconducting quantum hardware is expected to run into significant I/O restrictions due to the need for large-scale error-correction in a cryogenic environment. Classical data centers rely on fiber-optic interconnects to remove similar networking bottlenecks. In the same spirit, here we realize a radio-over-fiber qubit readout that does not require any active or passive cryogenic microwave equipment. We demonstrate all-optical single-shot readout by means of the Jaynes-Cummings nonlinearity in a circulator-free readout scheme. Specifically, we replace the complete cryogenic microwave input and output by an optical fiber and a single electro-optic transducer operated at mK temperatures. The latter is used simultaneously for demodulation of the input probing the qubit state as well as for modulation of the telecom light by means of the reflected microwave tone carrying information of the qubit state. We discuss the performance of this minimalistic readout, its implications on the qubit performance and its limitations. Even though the active optical heat load in the electro-optic link prevents substantial scaling-up of this first-generation implementation - importantly – we do not observe any direct impact of the laser light on the qubit performance, as verified with high-fidelity quantum-non-demolition measurements. This compatibility between superconducting circuits and light is not only a prerequisite to establish modular quantum networks, it is also relevant for multiplexed readout of superconducting photon detector or classical superconducting logic. Our experiment furthermore showcases the potential of electro-optic radiometry in harsh environments.   

Mechanical modes manipulation in magnomechanical and optomechanical hybrid system

Authours: Mai Zhang1,2,3, Guang-Ting Xu1,2,3, Yu Wang1,2, Zhen Shen1,2,3, Guang-Can Guo1,2,3, Chun-Hua Dong1,2,3.
1.CAS Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
2.CAS Center For Excellence in Quantum Information and Quantum Physics,University of Science and Technology of China, Hefei, Anhui 230088, People's Republic of China.
3.Hefei National Laboratory, University of Science and Technology of China, Hefei, Anhui 230088, People's Republic of China
Mechanical degrees of freedom, which have often been overlooked in various quantum systems, have been studied for applications ranging from quantum information processing to sensing. Here, we develop a hybrid platform to manipulate the mechanical degrees of freedom with magnetostrictive interaction and optically through the radiation pressure.

Phonon-based frequency combs that can be generated in the optical and microwave frequency domains have attracted much attention due to the small repetition rates and the simple setup. Via optomechanical or magnetostrictive interaction, we experimentally demonstrate a new type of phonon-based frequency comb in the magnomechanical or optomechanical hybrid system. Our demonstration offers an alternative phononic frequency comb for sensing, timing, and metrology applications.

When coherently coupling the magnomechanical system with an optomechanical system by straightway physical contact, the microwave-to-optical conversion with an ultrawide tuning range of up to 3 GHz can be realized. In addition, we observe a mechanical motion interference effect, in which the optically driven mechanical motion is canceled by the microwave-driven coherent motion. This effect shows that mechanical oscillators can be manipulated with equal facility through both magnonic and photonic channels.

Furthermore, the single excitation level strong coupling between the magnon modes and GHz phonon modes in magnonic films has been proved feasible in theory and the optomechanical coupling will be greatly enhanced by the small mode volume. Thus, this kind of integrated magnomechanical system will provide the tools to manipulate the mechanical degrees of freedom at a quantum level and enable new architectures for quantum information processing to sensing.   

Coherence studies of hundreds of overtone modes in a bulk acoustic wave resonator

High overtone bulk acoustic wave resonators (HBAR) have been successfully integrated with superconducting (SC) qubits into hybrid quantum systems that have many applications in quantum information technologies [1]. The coherences of HBAR modes have been extensively studied in relation to surface roughness, defect density, and other material properties [2]. However, the full multimode spectrum of HBARs in hybrid quantum systems has not yet been understood and characterised.

 

Here, we present a study of the coherence properties of hundreds of HBAR modes spanning several-GHz in frequency. Using a microwave antenna that is designed to electro-mechanically couple primarily to the Lagueurre-Gaussian (00) modes of the HBAR, we investigate the temperature and power dependence of the mode linewidths which allows us to quantify and distinguish various loss mechanisms. We also compare these results to measurements in the single-excitation regime using a SC qubit and find that, in both cases, there is a significant variation of lifetimes for different modes in a single HBAR device.

 

 

[1] U. von Lüpke et al. Parity measurement in the strong dispersive regime of circuit quantum acoustodynamics. Nat. Phys. 18, 794-799

 

[2] V. Gokhale et al. Epitaxial bulk acoustic wave resonators as highly coherent multi-phonon sources for quantum acoustodynamics. Nat. Commun. 11, 2314 (2020).   

Manufacturing large-scale high-yield hybrid superconducting-semiconducting on-chip cryogenic switches

We will present our latest progress in the development of quantum integrated circuits based on hybrid superconductor-semiconductor two-dimensional electron gas in InGaAs heterostructure. In particular, the design, nanofabrication, and cryogenic measurements of large-scale hybrid superconductor-semiconductor field-effect conductance switches with novel chip architectures will be discussed with a focus on their electronic response, switching (ON/OFF) statistics, quantum yield, and reproducibility. We demonstrate techniques for the successful fabrication of novel cryogenic gate voltage addressable nanoelectronics chips with negligible gate voltage leakage and with high switching response statistics, reproducibility rate, and quantum yields. We find that to make efficient cryogenic switches, the attention should especially be on the quality junction geometrical and interfacial parameters as the former influence the uniform switching voltages and the latter have a direct effect on the ON-OFF state conductance. The OFF state conductance is also a function of the quality oxide layers isolating the source-drain electrodes of hybrid junctions from split gate electrodes [1].  

[1] K Delfanazari et al., arXiv:2307.04355    

Enhancement of the coupling between a microwave photon and a color-center spin transition via a magnon mode

Hybrid quantum systems are attractive for emerging quantum technologies because they take advantage of the distinct properties of the constituent excitations; chiefly at the ultrastrong coupling regime, where the relaxation rates of the distinct quantum systems are exceeded by their coupling rate. Thus, a central challenge is to couple distinct quantum systems strongly, with all elements maintaining long coherence times. Magnetic materials are promising for coupling to long-lived quantum spin systems, potentially enabling quantum interconnects between important quantum technologies based on microwave photons and color-center spins (CCS). We describe an approach that dramatically enhances the effective coupling between microwave photons and CCS. Near the surface of a magnet, the color-center spins feel a strong dipole-dipole interaction with the nearby lattice of spin-polarized ions in the magnet. We predict that this microwave-magnon-spin coupling leads to an avoided crossing between the microwave photon and the CCS that dramatically exceeds the direct coupling between them.   

Surface phonon interference in hybrid quantum acoustic devices

Hybrid quantum systems based on surface acoustic wave (SAW) resonators coupled to superconducting qubits are being investigated for a variety of applications in quantum information processing. In these devices, surface phonon interference and scattering processes can alter the spectra of the mechanical modes and modify their interactions with coupled quantum systems [1]. This necessitates a more detailed investigation of phononic interference phenomenon in SAW-based hybrid systems. Here we report on the spectral analysis of a simple experimental system comprised of a SAW resonator galvanically coupled to a microwave transmission line. The entire device is fabricated on YZ-cut lithium niobate, and we are able to reveal the presence of interference effects of the surface phonon modes in the acoustic resonator over a broad range of temperature from 300K to 10mK. These measurements also allow us to extract the temperature dependent velocity for SAWs propagating on YZ-lithium niobate.

[1] Quantum acoustic Fano interference of surface phonons, J.M. Kitzman, J.R. Lane, C. Undershute, N.R. Beysengulov, C.A. Mikolas, K.W. Murch and J. Pollanen, Phys. Rev. A, 108, L010601 (2023).    

Reservoir engineered hybrid quantum systems

Recent developments in quantum engineering have given us the capability to design hybrid systems [1] with novel properties unseen in the regime they normally operate in. It is possible to couple multiple distinct systems to the same environment opening the possibility for non-equilibrium quantum dynamics to be exhibited. One such example arises when two individual spin ensembles (the first excited) are collectively coupled to the same reservoir. Superradiance emission [2] from the first ensemble followed by super absorption in the second leads to counter intuitive behavior where the second ensemble becomes excited (charged) and unable to decay to [3]. Such effects enables both quantum energy storage (quantum batteries) and transport. In this talk we will explore quantum energy and correlation transport through a network of ensembles collectively coupled to environments. Energy present at a specific node can migrate to a target node on much faster timescales than the single spin damping rate. Our approach will highlight the importance of being able to design and tailor the properties and symmetries of hybrid quantum systems and illustrate new future quantum technology directions.

[1] Z.-L. Xiang, S. Ashhab, J. Q. You, and F. Nori, Rev. Mod. Phys. 85, 623 (2013).

[2] R. H. Dicke, Phys. Rev. 93, 99 (1954).

[3] Y. Hama, W. J. Munro, and Kae Nemoto, Phys. Rev. Lett. 120, 060403 (2018)   

Hybrid Superconducting Qubit Based on Topological Insulator Junction

Superconducting quantum circuits offer a new platform to study quantum materials by leveraging the precise microwave control using the tools of circuit quantum electrodynamics (QED). Hybrid circuit devices incorporating novel quantum materials could also lead to new qubit functionalities like gate tunability and topological noise resilience. Here, we discuss progress towards a transmon-like qubit made with a superconductor-topological insulator-superconductor (S-TI-S) Josephson junction using exfoliated BiSbTeSe₂. We present a design that enables us to perform systematic characterization of the hybrid device, from DC transport of the S-TI-S junction, to RF spectroscopy, to full circuit QED control and detection of the hybrid qubit. In addition, we use a high quality-factor superconducting cavity to characterize material and fabrication-induced losses in our devices, to guide our efforts to improve the device quality. I will also discuss future plans to probe topological materials and excitations in our hybrid circuit platform.   

Measurement of Microwave Loss in Complex Oxide Heterostructures for Hybrid Quantum Systems

Hybrid microwave-acoustic systems at the quantum limit are emerging as a promising platform for the processing and storage of quantum information. In this area, piezo-acoustic cavities are of particular interest as they are capable of direct coupling of microwave to acoustic modes through piezoelectric modulation. However, creating a piezo-acoustic cavity requires on-chip integration of physically disparate piezoelectric and superconducting materials while maintaining a coherent behavior at microwave frequencies and milliKelvin (mK) temperatures. The extent of microwave loss in the piezoelectric elements within the cavities is specifically a point of concern. Here, we systematically study the microwave loss in epitaxial heterostructures of barium titanate (BTO)-on-silicon (BTO/Si) as a promising platform for piezo-acoustic cavities. We use a multi-resonator superconducting coplanar waveguide design as a pilot device to measure microwave losses at mK temperatures. By changing the thickness of various layers within the BTO/Si heterostructures including the buffer layers (e.g., YSZ, CeO2, STO, and LNO), we determine the contribution each oxide layer has to the overall loss of the heterostructure. Microwave transmission for each chip is measured at 30 mK-2 K with powers ranging from 0 to -60 dBm. The transmission spectra are then analyzed to extract the actual resonant frequency, quality factors (internal vs. external), and effective dielectric constant for each chip. The experimental work is complemented by COMSOL simulations that evaluate the electric field participation for each layer of the BTO/Si heterostructures.   

Time-domain Coherent Magnon Interference with On-chip Superconducting Hybrid Magnonic Circuits

Hybrid magnonic systems have recently emerged as a new promising direction that exploits the advantages of magnon excitations for processing quantum information [1]. Here, we develop a superconducting circuit platform, incorporating chip-mounted single-crystal YIG spheres that are mounted in lithographically defined holes on silicon substrates with superconducting resonators, for implementing microwave-mediated distant magnon-magnon interactions [2]. In particular, we use the two-YIG-sphere-one-superconducting-resonator system to demonstrate time-domain coherent magnon interference [3]. By sending a microwave pulse to one sphere and measuring the time trace of microwave output from the other antenna, we can measure the Rabi-like oscillation of magnon excitations between the two remote YIG spheres that are strongly coupled from their dispersive coupling to the superconducting resonator bus. In addition, we show that by sending two microwave pulses with a certainly time delay, their interactions to the YIG sphere lead to coherent interference, i.e. constructive or destructive interference depending on the relative phase delay of the two pulses. This allow us to program the magnon-magnon hybrid states by changing the frequency of the pulse microwave and the time delay. Our results provide a high-performance, circuit integrated cavity magnonic system for building coherent magnon networks and processing hybrid magnon excitations in the time domain.   

Oral: Towards Topological Magnons for Hybrid Magnonic Systems

Magnonic quantum hybrid systems have been proposed as a scheme to couple and entangle solid-state spin centers over micrometer lengths [1,2], improving the potential use of spin centers for quantum technologies. However, the required operating temperature for these hybrid schemes is ∼100mK, mainly due to the noise susceptibility of the magnetic excitations at high temperatures. This makes these systems less practical, barring their widespread application. Recently, it has been shown that one can harness the edge state localization of topological magnons to entangle spin qubits [3]. Here, we study the implementation of topological magnon modes for the entanglement of NV center qubits, paying special attention to the effect of differing edge state terminations. We begin by deriving topological magnons in 2D honeycomb ferromagnets in the presence of nearest neighbor and next nearest neighbor exchange, Dzyaloshinskii–Moriya interactions, and easy-axis anisotropy. Next, we develop a formalism for determining the coupling strength and relaxation time for NV-magnon interactions in bulk honeycomb ferromagnets. Finally, we present our results on the coupling between NV centers and topological magnons in different nanoribbons, and comment on how this formalism allows us to predict the fingerprint of topological magnons via quantum sensors.

[1] D. R. Candido et al 2021 Mater. Quantum. Technol. 1 011001

[2] M. Fukami et al PRX Quantum 2, 040314 (2021)

[3] B. Hetényi et al Phys. Rev. B 106, 235409 (2022)   

Small-mode-volume surface-acoustic-wave resonators with focused Gaussian beam modes.

Hybrid devices using surface-acoustic-wave (SAW) resonators offer a platform for exploring the coherent couplings between acoustic waves and other quantum systems. To increase the coupling in such systems, reducing the resonator mode volume is effective. However, conventional SAW resonators with parallel interdigitated electrodes face increasing diffraction loss with decreasing acoustic mode width. To minimize the in-plane mode volume while suppressing diffraction loss, focusing-type SAW resonators are used in analogy with the Gaussian beam in an optical resonator. It focuses the wavefront of the SAW mode and narrows the beam near the center of the device [1]. Nevertheless, the design principle of such focused resonators has not been established, and the device geometry that allows selective excitation of the fundamental resonance mode has not been clarified.

In this study, we fabricated the focused SAW resonators with electrodes of various curvatures and lengths to clarify the correspondence between the resonator designs and the resonance modes. The microwave transmission revealed multiple resonance peaks, and their number systematically correlated with the curvature of the electrodes. These modes were identified as the fundamental Gaussian mode and higher-order transverse modes. Furthermore, by adjusting the length of the electrodes, we selectively fabricated a single-mode resonator with only the fundamental mode and a multi-mode resonator with higher-order transverse modes.

[1] S. J. Whiteley et al., Nat. Phys. 15, 490–495 (2019).   

Decoherence of surface phonons in the weak dispersive regime of circuit quantum acoustodynamics

Circuit quantum acoustodynamic (cQAD) systems are ideal for investigating the quantum properties of mechanical resonators by leveraging the intrinsic nonlinearity of superconducting qubits. Here we describe an experiment in which the electro-mechanical response of a surface acoustic wave (SAW) device enables the realization of an open cQAD system. The hybrid system is implemented via capacitive coupling between a 3D transmon qubit and a custom-designed SAW device. This device architecture allows for the transmon to simultaneously couple strongly to a resonant SAW mode and also weakly with non-resonant, lossy surface phonon modes. By populating the SAW device with phonons and then dispersively reading out its state via the qubit, we are able to measure the dynamics and decoherence of the surface phonon states in the resonator. In this fashion, with a single device, we can measure the decoherence of phonons in the resonant mode, and use the broader SAW phonon spectrum to investigate the decoherence of the hybrid system.