arXiv subjects

Michael Senatore

Publications and source records attributed to Michael Senatore.

7 recordsLinked to original sources

arXiv2026

High-fidelity iSWAP gate with Double Transmon Coupler

Entangling operations are at the heart of all approaches to quantum information processing. Parametric gates, in particular, offer a versatile solution to strongly couple off-resonant superconducting qubits with suppressed parasitic crosstalk to spectator qubits due to frequency-selective activation. In this work, we demonstrate a parametric iSWAP gate between two transmon qubits using the recently developed double transmon coupler (DTC). The DTC supports robust internally-defined cancellation point (``off'' state) for static interactions, while simultaneously mediating a fast parametric coupling between data qubits that can be deployed for high-fidelity two-qubit operations. We use robust phase estimation to calibrate non-commuting error terms in the parametric iSWAP gate, and achieve a 99.827% gate fidelity in 40ns without any numerical optimization. The circuit architecture and calibration techniques developed here are extensible to other gate implementations and qubit modalities, paving the way towards resource-efficient quantum information processing.

quant-ph↗

arXiv2026

Transmon Architecture for Emission and Detection of Single Microwave Photons

We develop a compact transmon emitter/detector (TED) superconducting circuit and demonstrate its dual functionality as a single-photon source and detector. In our setup, photons emitted by a source TED are transmitted via a meter-long coaxial cable, routed through a circulator, and captured by a measurement TED. Both TED modules operate with nominally identical parameters, highlighting the flexibility of this novel architecture. Furthermore, we introduce an efficient microwave photon detection scheme tailored to the TED. Using this setup, we detect 60% of the emitted Fock state photons and infer a 95% detection efficiency at the input of the measurement TED, which we calibrate against coherent state measurements. The reset and photon emission/detection processes each require approximately $2\,\mu s$, yielding a minimum protocol duration of $4\,\mu s$ as constrained by our chosen TED parameters. Ultimately, the TED demonstrates a new use case for the recently developed double transmon coupler (DTC): a compact, drop-in, tunable, and transition-selective link between a coherent data transmon and a waveguide. Circuits like the TED will play a vital role in quantum information processing by facilitating unconditional fast reset, enabling microwave photon metrology, and serving as nascent quantum communication interfaces (QCIs). QCIs mediate entanglement distribution between quantum processing units (QPUs) within a cryostat or interface with microwave-to-optical transducers for long-range quantum networking.

quant-ph↗

arXiv2025

Ta-based Josephson junctions using insulating ALD TaN tunnel barriers

Josephson junctions form the core circuit element in superconducting quantum computing circuits, single flux quantum digital logic circuits, and sensing devices such as SQUIDs. Aluminum oxide has typically been used as the tunnel barrier. Its formation by exposure to low oxygen pressures at room temperature for short periods of time makes it susceptible to aging and limits the thermal budget of downstream processes. In this paper, we report the first demonstration of {\alpha}-Ta/insulating TaN/a-Ta superconductor/insulator/superconductor Josephson junctions fabricated on 300 mm wafers using CMOS-compatible processes. The junctions were fabricated on high-resistivity silicon substrates using standard processes available at 300 mm scale, including 193 nm optical lithography, ALD of TaN in a cluster tool, and chemical mechanical planarization to enable highly planar interfaces. Junction areas ranging from 0.03 um2 to 9 um2 with ALD TaN thickness between 2 nm and 7 nm were characterized. A critical current density of 76 uA/um2 was observed in junctions using 4 nm ALD TaN in the tunnel barrier. The dependence of Jc on ALD TaN layer thickness is analyzed, and the influence of junction geometry, packaging, and temperature on I-V characteristics is discussed. Junctions were retested after a period of 4 months to quantify junction aging. The potential of this novel material system and a 300 mm superconducting junction process flow to fabricate thermally and environmentally stable junctions is discussed. The vision of a Superconducting Quantum Process Design Kit for a Multi-Project Wafer program to enable rapid development and proliferation of superconducting quantum and digital digital logic systems is presented. This work represents the first step towards establishing such a Quantum Foundry, providing access to high quality qubits and single-flux quantum logic circuits at 300 mm wafer scale.

cond-mat.supr-con↗

arXiv2025

Fast Recovery of Niobium-based Superconducting Resonators after Laser Illumination

Interfacing superconducting microwave resonators with optical systems enables sensitive photon detectors, quantum transducers, and related quantum technologies. Achieving high optical pulse repetition is crucial for maximizing the device throughput. However, light-induced deterioration, such as quasiparticle poisoning, pair-breaking-phonon generation, and elevated temperature, hinders the rapid recovery of superconducting circuits, limiting their ability to sustain high optical pulse repetition rates. Understanding these loss mechanisms and enabling fast circuit recovery are therefore critical. In this work, we investigate the impact of optical illumination on niobium nitride and niobium microwave resonators by immersing them in superfluid helium-4 and demonstrate a three-order-of-magnitude faster resonance recovery compared to vacuum. By analyzing transient resonance responses, we provide insights into light-induced dynamics in these superconductors, highlighting the advantages of niobium-based superconductors and superfluid helium for rapid circuit recovery in superconducting quantum systems integrated with optical fields.

quant-ph↗

arXiv2025

Noise-Aware Entanglement Generation Protocols for Superconducting Qubits with Impedance-Matched FBAR Transducers

Connecting superconducting quantum processors to telecommunications-wavelength quantum networks is critically necessary to enable distributed quantum computing, secure communications, and other applications. Optically-mediated entanglement heralding protocols offer a near-term solution that can succeed with imperfect components, including sub-unity efficiency microwave-optical quantum transducers. The viability and performance of these protocols relies heavily on the properties of the transducers used: the conversion efficiency, resonator lifetimes, and added noise in the transducer directly influence the achievable entanglement generation rate and fidelity of an entanglement generation protocol. Here, we use an extended Butterworth-van Dyke (BVD) model to optimize the conversion efficiency and added noise of a Thin Film Bulk Acoustic Resonator (FBAR) piezo-optomechanical transducer. We use the outputs from this model to calculate the fidelity of one-photon and two-photon entanglement heralding protocols in a variety of operating regimes. For transducers with matching circuits designed to either minimize the added noise or maximize conversion efficiency, we theoretically estimate that entanglement generation rates of greater than $160\;\mathrm{kHz}$ can be achieved at moderate pump powers with fidelities of $>90\%$. This is the first time a BVD equivalent circuit model is used to both optimize the performance of an FBAR transducer and to directly inform the design and implementation of an entanglement generation protocol. These results can be applied in the near term to realize quantum networks of superconducting qubits with realistic experimental parameters.

quant-ph↗

arXiv2024

Fast single-qubit gates for continuous dynamically decoupled systems

Environmental noise that couples longitudinally to a quantum system dephases that system and can limit its coherence lifetime. Performance using quantum superposition in clocks, information processors, communication networks, and sensors depends on careful state and external field selection to lower sensitivity to longitudinal noise. In many cases time varying external control fields--such as the Hahn echo sequence originally developed for nuclear magnetic resonance applications--can passively correct for longitudinal errors. There also exist continuous versions of passive correction called continuous dynamical decoupling (CDD), or spin-locking depending on context. However, treating quantum systems under CDD as qubits has not been well explored. Here, we develop universal single-qubit gates that are ``fast'' relative to perturbative Rabi gates and applicable to any CDD qubit architecture. We demonstrate single-qubit gates with fidelity $\mathcal{F}=0.9947(1)$ on a frequency tunable CDD transmon superconducting circuit operated where it is strongly sensitive to longitudinal noise, thus establishing this technique as a potentially useful tool for operating qubits in applications requiring high fidelity under non-ideal conditions.

quant-ph↗

arXiv2022

Modular tunable coupler for superconducting qubits

The development of modular and versatile quantum interconnect hardware is a key next step in the scaling of quantum information platforms to larger size and greater functionality. For superconducting quantum systems, fast and well-controlled tunable circuit couplers will be paramount for achieving high fidelity and resource efficient connectivity, whether for performing two-qubit gate operations, encoding or decoding a quantum data bus, or interfacing across modalities. Here we propose a versatile and internally-tunable double-transmon coupler (DTC) architecture that implements tunable coupling via flux-controlled interference in a three-junction dcSQUID. Crucially, the DTC possesses an internally defined zero-coupling state that is independent of the coupled data qubits or circuit resonators. This makes it particular attractive as a modular and versatile design element for realizing fast and robust linear coupling in several applications such as high-fidelity two-qubit gate operations, qubit readout, and quantum bus interfacing.

quant-ph↗