Session F53: Quantum Optomechanics and Transducers

An electro-opto-mechanical transducer implementation for downconversion of squeezed states of light

Creating an entangled network of superconducting quantum nodes connected by optical links is a major goal in the fields of quantum computing and networking. Towards this goal, different quantum transducer platforms are the focus of ongoing optimization across multiple inter-connected figures of merit. Our device uses a macroscopic mechanical mode of a Si₃N₄ membrane as an intermediary, to couple a superconducting LC circuit to a high finesse optical Fabry-Perot cavity for carrying out efficient and low noise frequency conversion across 5 orders of magnitude.  Here, we present our ongoing experimental progress towards operating one of these converter devices with the goal of connecting a squeezed light source to the optical input, and preserving the quantum correlations after conversion to microwave frequencies.   

Efficient numerical simulation of microwave-optical quantum transducers

For realization of quantum network, one of promising options is to convert microwave photon qubits, which are used in local superconducting processors, into optical photon qubits, which travel in the optical fibers connecting the remote processors. While devices so called quantum transducers will enable us such a conversion, their development is challenging since each of them is a hybrid system composed of a superconducting circuit, a mechanical resonator, a solid-state qubit, an optical cavity etc. To design a transducer, we need to have a detailed numerical simulation for the conversion process, such as the dependence of the output fields on the pulse shape of the input fields, the power spectrum, and coherent conversion rates. In our work, we have simulation for the above properties on two devices, one with an optomechanical crystal and the other with a diamond optomechanical crystal with a color center. We evaluate the power spectrum with a pulsed input by one-time correlator of an auxiliary resonator operator, which greatly reduces the computational cost, since standard methods require the evaluation of two-time correlators.   

Efficiency and noise characterization of an on-chip microwave to optical transducer using 171Yb3+: YVO4 crystals

Microwave-to-optical transduction is essential for large-scale quantum networks and distributed quantum computing based on superconducting qubits. Rare-earth ion (REI) ensemble is one of the promising systems because of the narrow inhomogeneous linewidth in both optical and spin domain at cryogenic temperature, which provides strong nonlinearities for facilitating the interaction between microwave and optical fields. Ytterbium-171 is of special interest because of its strong dipole moment and simplest hyperfine structure.

Here, we present our on-going efforts on an on-chip REI-based microwave to optical transducer using ¹⁷¹Yb³⁺: YVO₄, with integrated superconducting microwave resonators and gold reflectors. The microwave resonator was fabricated out of niobium on top of ¹⁷¹Yb³⁺: YVO₄ substrate. A thin layer of gold was evaporated on the back of the chip for light collection. We characterized the transducer performance at dilution temperature. Strong coupling between the resonator and excited state spin was observed. We calibrated efficiencies in both continuous-wave mode and pulsed mode. The added noise during pulsed operations was measured on a single photon detector. We’ll discuss the future directions as well in the presentation.

The authors acknowledge support from Office of Naval Research Award No. N00014-22-1-2422 and U.S. Department of Energy, Office of Science, National Quantum Information Science Research Centers, Codesign Center for Quantum Advantage (contract number DE-SC0012704).   

Millimeter-Wave to Telecom Electro-Optic Frequency Transduction on Thin-Film Lithium Niobate

Electro-optic frequency transduction of microwave-to-optical photons is one promising avenue for linking cryogenic quantum nodes. In particular, millimeter wave (mmW) superconducting systems at high frequencies (~105 GHz) enable high microwave-optical photon couplings and greater pump-power compared to lower-frequency (~5 GHz) transduction. We demonstrate this technology via triply-resonant mmW (~105 GHz) to telecom (~193 THz) frequency conversion. Our device consists of a NbTiN mmW resonator atop thin-film lithium niobate, with a sapphire substrate. In our preliminary results, we study the coupling rate between optical and mmW photons and determine conversion efficiency. As next steps, we aim to study converted sideband asymmetry for mode thermometry and other optomechanical phenomena in the mmW regime. Our work demonstrates a first step toward coherent microwave-to-optical transduction mediated by mm-waves.   

Microwave-to-Optical Quantum Transduction Utilizing the Topological Magnetoelectric Effect

The quantum transduction (or equivalently quantum frequency conversion) between microwave and optical photons is essential for realizing scalable quantum computers with superconducting qubits. Due to the large frequency difference between microwave and optical ranges, the transduction needs to be done via intermediate bosonic modes or nonlinear processes. In this study, we focus on the transduction via the magneto-optic Faraday effect, i.e., the light-magnon interaction. Previous experimental studies have demonstrated the transduction efficiency of O(10^-8 - 10^-10) by using the ferromagnet YIG and have shown that the transduction efficiency is essentially determined by the light-magnon interaction strength. Here, we take advantage of the fact that three-dimensional topological insulator thin films exhibit a universal Faraday rotation angle arising from the topological magnetoelectric effect. This leads to a large Faraday rotation angle and therefore enhanced light-magnon interaction in the thin-film limit. We show theoretically that the transduction efficiency can be greatly improved to O(10^-4) by utilizing a heterostructure of a few dozen of layers consisting of topological insulator thin films such as Bi₂Se₃ and ferromagnetic insulator thin films such as YIG.   

Wide-band, tunable and high-efficiency microwave-to-acoustics transduction on lithium niobate

Acoustic waves play an essential role in a wide variety of quantum systems such as microwave-to-optics transducers, quantum acoustics devices or devices using strain to couple to spin defects. For surface acoustic waves and Lamb waves, control and detection are commonly achieved using interdigital transducers (IDTs) on piezoelectric materials. However, due their frequency dependent impedance, IDTs can only be efficient over narrow bandwidths.

 

We propose a wide-band high-efficiency transducer to perform microwave-to-acoustics transduction where an interdigital transducer (IDT) is used to couple to Lamb waves in suspended Lithium Niobate. By using a SQUID array, we design a magnetic flux tunable impedance matching network that optimizes power conversion at the IDT despite its frequency dependent impedance.

Measurements at cryogenic temperatures show that this bi-directional transducer can reach high efficiencies over large bandwidths (typically 400 MHz) and can be tuned over a wide frequency band (4-8GHz).  This device is a building block for quantum acoustics experiments and could be used to perform the acoustic spectroscopy of quantum objects or couple superconducting qubits to mechanical degrees of freedom.   

Nonlinear Microwave-optical Quantum Transduction

Microwave-optical quantum transducers are an essential part of building quantum networks as they allow remote microwave-based superconducting quantum processors to be connected by optical photons. Many transduction schemes that directly convert between the two frequency regimes have been proposed, but transduction can also be realized through quantum teleportation with entangled microwave-optical photon pairs, which has been shown to out-perform direct transduction within experimentally feasible regimes. Current entanglement-based transduction relies on the Spontaneous Parametric Down Conversion (SPDC) process to generate reliable entanglement, which could introduce unwanted double-photon pairs in the output. Here we study the possibility of generating pure single-photon pairs using SPDC with strong Kerr nonlinearity. Differing from the traditional continuous variable approach, we construct the Non-Gaussian output by cascading the emission to virtual cavities with time-dependent couplings, and show that the probability of higher order processes are suppressed exponentially with the increase of Kerr strength. To compare with the photon emission of SPDC, we also calculate the emission rate and the Glauber second order coherence function as figures of merits.    

Measurements of cryogenic mirror thermal noise and its impact on quantum electro-opto-mechanical transducers

A sufficiently efficient and low-noise transducer linking microwave and optical frequencies would enable entanglement between superconducting quantum registers separated by long distances. We have previously shown highly efficient and near-quantum transduction by coupling a mechanical mode of a Si₃N₄ membrane simultaneously to a superconducting LC circuit and a high finesse optical Fabry-Perot cavity. Even with large transduction efficiencies, total losses between an attached qubit and the optical readout port would prohibit direct entanglement of superconducting registers. Single-photon readout can be leveraged to tradeoff success probability for entanglement fidelity when confronted with these losses, albeit at the expense of increased sensitivity to noise that is spectrally broader than the transducer bandwidth. In this talk we will discuss how broadband thermal noise from our cryogenically cooled Fabry-Perot mirrors contributes to noise during single-photon readout. We will present measurements of this noise in a dry cycle dilution refrigerator and discuss attempts to suppress the noise by operating phonically filtered mirrors at cryogenic temperatures.   

Microwave-optical transduction at milli-Kelvin temperatures using hybrid bulk acoustic resonances

Efficient microwave-optical quantum conversion is necessary for the large-scale integration of superconducting qubits into telecom fiber-optic networks and heterogeneous quantum networking hardware. Here, we study a piezo-optomechanical transducer based on hybrid bulk acoustic resonances (HBARs)[1-3] in a dilution refrigerator at 10 mK. Optical and microwave drives are pulsed to enable high peak pump powers while minimizing the local thermal load on the transducer. We will present our latest measurements characterizing the conversion efficiency of this new platform and discuss next steps in boosting the efficiency, including experimental upgrades and investigating new devices with higher optomechanical coupling.

[1] H. Tian et al. Nature Communications volume 11, 3073 (2020)

[2] T. Blesin et al. Phys. Rev. A 104, 052601 (2021)

[3] T. Blesin et al. arXiv:2308.02706 (2023)   

Electromechanical cooperativity greater than 1,000 in an electro-opto-mechanical transducer

Realizing a network of superconducting quantum computational nodes connected over long distances by optical fibers will require a highly efficient and low-noise microwave-to-optical transducer. A mechanical mode of a Si3N4 membrane simultaneously coupled to a superconducting LC circuit and a high finesse optical Fabry-Perot cavity can mediate transduction between the electromagnetic modes with the help of strong parametric pumps. Our implementation of such a transducer has achieved 47% efficiency and only 3.2 photons of input-referred added noise in up-conversion [1]. Surpassing the quantum threshold of 1 photon of added noise can be achieved by optimization of the microwave cavity loss rate, the technical noise induced by the microwave pump, and the electromechanical coupling rate. Here, we present progress on these optimizations with the goal of ground-state cooling the mechanical mode with the electromechanical interaction, a necessary requirement for quantum-enabled microwave-to-optical transduction.

[1] Brubaker, B. M., Kindem, J. M., Urmey, M.D, et. al., Optomechanical Ground-State Cooling in a Continuous and Efficient Electro-Optic Transducer, Phys. Rev. X 12, 021062   

Coherent microwave single-photon source for a mechanically mediated electro-optic transducer

A low-noise and highly efficient transducer is a crucial piece to interface two superconducting qubits from distant places. However, generating a high-coherence quantum state matched to the transducer’s kHz bandwidth is quite challenging since it requires a long pulse duration. In this talk, I will present our experimental effort to build a coherent quantum source for our mechanically-mediated transducer. This single-photon source comprises two 3d cavities and a transmon qubit, and the transmon both provides the nonlinearity for generating single-photon state and acts as a four-wave mixing element for swapping the quantum state between these two cavities.   

Acoustic probing of spin-phonon interactions for solid-state defects in the quantum regime.

Understanding spin-phonon interactions is essential for solid-state quantum technologies that exploit the spin degree of freedom. Experimental probes for spin-phonon interaction in the quantum regime are therefore needed. We develop a versatile technique to probe the resonant coupling of solid-state defects to strain in the absence of thermal motion. Our technique consists in measuring high overtone frequency bulk acoustic wave resonators (HBAR) at 50 mK, in crystals hosting spin defects. By bonding a thin-film lithium niobate transducer onto the host crystal, we couple to its HBAR modes at GHz frequencies. Preliminary results demonstrate that we observe the characteristic acoustic response of HBAR structures and show the potential to measure spin-strain coupling for various crystal targets. This technique could be use to identify spin species suitable to acheive coherent spin-phonon interactions.   

Coherently driving a single nuclear spin through the resonance of a nanomechanical oscillator

The discovery of nuclear electric resonance in a single ¹²³Sb nucleus in silicon [1] was accompanied by a detailed, quantitative understanding of the coupling between the nuclear quadrupole moment and lattice strain. With this knowledge, it is possible to design an experiment where the nuclear spin is coherently controlled using resonant acoustic drive, i.e. nuclear acoustic resonance (NAR) [2]. In this work we present a more advanced spin-mechanical device where the dynamical strain induced at the clamping point of a resonating nanoscale cantilever is used to drive single-nucleus NAR, and illustrate a method of electrically detecting the resonant frequency of the nanocantilever. Taken to the extreme, this design could be adapted to demonstrate the strong coupling between a single nuclear spin and a single phonon in a mechanical resonator, with exciting ramifications in foundational experiments on quantum mechanics.

 

[1] S. Asaad et al., Nature 579, 205 (2020)

[2] L. A. O’Neill et al., Appl. Phys. Lett. 119, 174001 (2021)   

Optomechanical quantum bus for donor spins in silicon

Donor spins in silicon are a promising platform for quantum information, combining good quantum properties (coherence times, gate fidelities) with the strong industrial know-how of silicon fabrication. Their application potential is, however, somewhat constrained by the lack of an optical interface, and considerable attention has been recently focused on spin-photon interfaces in silicon. Unfortunately, the most studied and best-known donor qubits (phosphorous, bismuth) do not possess optical transitions.

To address this, we aim to develop an optomechanical bridge between the donor spin qubits and telecom-wavelength photons. We couple the spin qubit to the mechanical motion of a nanoresonator, whose motion in turn influences the resonance frequency of an optical cavity. This allows reading out the qubit state with a telecom wavelength laser. The mechanical system can also be used to couple spins to each other in a controlled way.

 

In this talk, I will present the fundamental concepts for such a proposal and numerical simulations regarding its implementation in a practical system of silicon nanobeams implanted with donors. I will also present preliminary experimental data on our current progress towards characterizing the optomechanical resonators with embedded spins [1] and developing auxiliary spin readout methods [2] to be used with the nanobeams.

[1] C. Shakespeare et al., Mater. Quantum. Technol. 1, 045003 (2021)

[2] T. Loippo et al, Phys. Rev. Materials 7, 016202 (2023).