Scaling superconducting quantum processors to large qubit counts faces challenges in control-signal delivery, thermal management, and hardware complexity, particularly in achieving microwave signal multiplexing and long-distance quantum information routing at millikelvin temperatures. We propose a space-time modulated Josephson-junction metasurface architecture to generate and multiplex microwave control signals directly at millikelvin temperatures. Theoretical and numerical results demonstrate the generation of multiple frequency tones with controlled parameters, enabling efficient and scalable qubit control while minimizing thermal loads and wiring overhead. We derive the nonlinear wave equation governing this system, simulate beam steering and frequency conversion, and discuss the feasibility of experimental implementation. These results lay the groundwork for a next-generation cryogenic signal-delivery paradigm that may enable scaling of superconducting quantum processors to thousands of qubits without overwhelming limited dilution-refrigerator cooling power.
Scaling superconducting quantum processors to large qubit counts faces challenges in control-signal delivery, thermal management, and hardware complexity, particularly in achieving microwave signal multiplexing and long-distance quantum information routing at millikelvin temperatures. We propose a space-time modulated Josephson-junction metasurface architecture to generate and multiplex microwave control signals directly at millikelvin temperatures. Theoretical and numerical results demonstrate the generation of multiple frequency tones with controlled parameters, enabling efficient and scalable qubit control while minimizing thermal loads and wiring overhead. We derive the nonlinear wave equation governing this system, simulate beam steering and frequency conversion, and discuss the feasibility of experimental implementation. These results lay the groundwork for a next-generation cryogenic signal-delivery paradigm that may enable scaling of superconducting quantum processors to thousands of qubits without overwhelming limited dilution-refrigerator cooling power.
Abstract We introduce space-time-modulated cryogenic-compatible Josephson metasurfaces as a versatile platform for polychromatic qubit coupling and frequency-selective interactions. These metasurfaces, based on arrays of gated superconductor-semiconductor Josephson field-effect transistors (JoFETs), enable dynamic four-dimensional (space-time) control of microwave fields at millikelvin temperatures. Through spatiotemporal modulation of the critical current density, the metasurface generates controllable Floquet harmonics, facilitating frequency conversion, parametric amplification, and nonreciprocal propagation. Full-wave electromagnetic simulations demonstrate selective excitation and multi-frequency state transitions in superconducting qubit arrays, where a photon emitted at frequency is efficiently redirected into multiple target frequencies to mediate long-range interactions between adjacent and non-adjacent qubits. In the circuit quantum electrodynamics framework, this yields an effective polychromatic Hamiltonian supporting frequency-multiplexed exchange couplings while providing spectral isolation that suppresses crosstalk. The engineered non-Markovian environment arising from the space-time modulation offers pathways to enhance qubit coherence times and entanglement fidelity through information backflow and noise suppression. Fabrication pathways using Al-proximitized InAs quantum wells and cryogenic measurement setups are discussed. This work establishes space-time-modulated Josephson metasurfaces as promising hardware enablers for frequency-selective control, improved connectivity, and robust operation in next-generation superconducting quantum systems.
Superconducting quantum circuits operate at millikelvin temperatures, typically requiring independent microwave cables for each qubit for connecting room-temperature control and readout electronics. However, scaling to large-scale processors hosting hundreds of qubits faces a severe input/output (I/O) bottleneck, as the dense cable arrays impose prohibitive constraints on physical footprint, thermal load, wiring complexity, and cost. Here we demonstrate a complete optical I/O architecture for superconducting quantum circuits, in which all control and readout signals are transmitted exclusively via optical photons. Employing a broadband traveling-wave Brillouin microwave-to-optical transducer, we achieve simultaneous frequency-multiplexed optical readout of two qubits. Combined with fiber-integrated photodiode arrays for control signal delivery, this closed-loop optical I/O introduces no measurable degradation to qubit coherence times, with an optically driven single-qubit gate fidelity showing only a 0.19% reduction relative to standard microwave operation. These results establish optical interconnects as a viable path toward large-scale superconducting quantum processors, and open the possibility of networking multiple superconducting quantum computers housed in separate dilution refrigerators through a centralized room-temperature control infrastructure.
The pursuit of scalable and robust quantum computing necessitates innovative approaches to overcome the inherent challenges of qubit connectivity, decoherence, and susceptibility to noise and crosstalk. Conventional monochromatic qubit coupling architectures, constrained by nearest-neighbor interactions and limited algorithmic flexibility, exacerbate these issues, hindering the realization of practical large-scale quantum processors. In this work, we introduce a paradigm leveraging a space-time-modulated cryogenic-compatible Josephson metasurface to enable polychromatic qubit coupling. This metasurface facilitates frequency-selective interactions, transforming nearest-neighbor connectivity into all-to-all qubit interactions, while significantly enhancing coherence, noise robustness, and entanglement fidelity. Our proposed approach capitalizes on the unique capabilities of space-time-modulated Josephson metasurfaces, including dynamic four-dimensional wave manipulation, nonreciprocal state transmission, and state-frequency conversion, to mediate multi-frequency qubit interactions. By isolating qubit couplings into distinct spectral channels, the cryogenic-compatible metasurface mitigates crosstalk and environmental decoherence, extending coherence times and preserving quantum state fidelity. Full-wave simulations and quantum performance analyses demonstrate a significant enhancement in the operational efficiency of a superconducting qubit array, showcasing improved connectivity, robustness, and entanglement stability. This study establishes the potential of space-time-modulated cryogenic-compatible Josephson metasurfaces as a transformative platform for next-generation quantum computing, addressing critical bottlenecks and paving the way for scalable, high-performance quantum processors.
Scaling quantum processors requires cryogenic microwave components to minimize thermal load and wiring complexity. However, conventional microwave components such as mixers and phase shifters perform poorly at millikelvin temperatures. Here, we report an SrTiO 3 (STO)-based microwave frequency mixer and phase shifter operating at sub-Kelvin temperatures. Utilizing the effective χ (2) nonlinearity of STO in the quantum paraelectric state, induced by a static or oscillating field, we achieve efficient microwave frequency mixing. Our device features an aluminum superconducting coplanar waveguide resonator on STO, which resonantly enhances mixing characteristics. The exceptionally high field-tunable dielectric constant of STO—approximately 30,000—allows for highly compact architectures and facilitates voltage-controlled phase shifting. Furthermore, we demonstrate multi-tone frequency mixing via phase modulation, facilitating spectral filtering and shaping. These STO-based devices provide a transformative approach to the generation of intricate microwave waveforms, tailoring control and readout signals in multi-qubit systems and paving the way for co-located quantum-classical integration.
As quantum computing technology advances, the demand for efficient, scalable, and thermally optimized solutions for qubit control and readout under cryogenic conditions has become increasingly critical. Currently, cryogenic qubit systems rely on numerous coaxial cables and DC wires for readout and control—typically two to three per qubit. Such dense wiring introduces significant engineering challenges, particularly regarding heat dissipation and spatial limitations [1]. To address these issues, wireless approaches have been proposed, offering promising advantages in scalability, thermal load reduction, and efficient quantum state transfer. Although wireless systems eliminate the need for cables, dilution refrigerators (DRs) impose strict spatial constraints, limiting the use of conventional microwave-range wireless components such as horn antennas and dielectric lenses. In addition, the sensitive and enclosed cryogenic environment demands precise beam shaping to prevent unwanted scattering and reflections. Hence, there is a pressing need for a compact and effective wireless solution tailored to such environments. In this study, we present a next-generation wireless communication system specifically designed for cryogenic quantum environments, enabling qubit control and readout at millikelvin temperatures. To achieve optimal signal transmission, we explored and simulated multiple design strategies, addressing challenges such as signal degradation, noise interference, and limited spatial volume within the refrigerator. Our system employs metasurface lens antennas to enhance transmission efficiency while minimizing signal-to-noise ratio (SNR) degradation. Considering the confined geometry of cryogenic setups, we developed two types of compact metalens antennas operating in both the microwave and millimeterwave regimes. Experimental measurements demonstrate more than 20 dB enhancement in wireless transmission, consistent with simulation results. These findings confirm that the proposed system satisfies the stringent requirements of quantum control and readout, making it a promising and practical solution for future quantum computing applications. We will share further details and insights on the metasurface-enabled wireless quantum computing platform at the upcoming conference presentation.
For superconducting quantum processors, microwave signals are delivered to each qubit from room-temperature electronics to the cryogenic environment through coaxial cables. Limited by the heat load of cabling and the massive cost of electronics, such an architecture is not viable for millions of qubits required for fault-tolerant quantum computing. Monolithic integration of the control electronics and the qubits provides a promising solution, which, however, requires a coherent cryogenic microwave pulse generator that is compatible with superconducting quantum circuits. Here, we report such a signal source driven by digital-like signals, generating pulsed microwave emission with well-controlled phase, intensity, and frequency directly at millikelvin temperatures. We showcase high-fidelity readout of superconducting qubits with the microwave pulse generator. The device demonstrated here has a small footprint, negligible heat load, great flexibility to operate, and is fully compatible with today's superconducting quantum circuits, thus providing an enabling technology for large-scale superconducting quantum computers.