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Cell Reports Physical Science

Cryogenic microwave mixing and phase control in superconducting quantum paraelectric resonator

H. Sundaresan, Prasad Muragesh, Madhu Thalakulam

Published Jun 10, 2026• 0 citations
Publisher

Abstract

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.

DOI
10.1016/j.xcrp.2026.103387

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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.
A frequency comb, known for its precision as an “optical ruler,” features an evenly spaced spectral pattern. While these combs are vital in integrated photonics, their microwave counterparts are now highly sought in cryogenic quantum technologies, including semiconducting and superconducting qubits as well as quantum electrical metrology. However, microwave combs are still largely underexplored. Existing studies mostly rely on complex, high-power optical systems incompatible with the low-power, cryogenic on-chip architecture. In this manuscript, we present an all-electrical, on-chip, cryogenic microwave frequency comb on strontium titanate (SrTiO3), exploiting its Pockels-like effect in its quantum paraelectric phase. Our device utilizes a superconducting microwave cavity to generate the frequency comb via cavity phase modulation enabled by the field-induced effective χ(2) of SrTiO3. The ability to continuously vary the dielectric constant of SrTiO3 by the application of an electric field, in its quantum paraelectric phase, makes it possible to control the comb's operating frequency span. The exceptionally high dielectric constant of SrTiO3, > 20 000 at low temperatures, enables an ultra-miniature design and on-chip integration with cryogenic quantum technologies.
At cryogenic temperatures and microwave frequencies, the perovskite crystals strontium titanate (STO) and potassium tantalate (KTO) have large, tunable permittivity arising from a quantum paraelectric phase. As such, these materials hold promise as a platform to realize compact, variable capacitance elements for use in quantum devices. From modulating this capacitance, we propose the development of a parametric mixing element: a quantum paraelectric nonlinear dielectric amplifier (PANDA). We calculate that a PANDA made from a nanofabricated parallel plate capacitor and realistic design constraints can demonstrate a three-wave mixing strength of order MHz, in comparison to an effective Kerr strength of sub-Hz. This suggests excellent performance as a three-wave mixing element, with high compression power in analogy to superconducting parametric amplifiers based on kinetic inductance. Beyond parametric amplifiers, we predict that compact, tunable capacitors based on STO, KTO, and related materials can enable a wide class of cryogenic quantum circuits including novel filters, switches, circulators, and qubits.
Here, we demonstrate an on-chip cryogenic microwave frequency-comb on a planar superconducting resonator fabricated on Strontium titanate(STO), a quantum paraelectric material. The material's Kerr-type nonlinearity arising from the quantum paraelectric phase, an underexplored state, enables pronounced resonance shifts, Duffing-like bifurcations and comb generation via cascaded foure-wave mixing. Our results establish STO resonators as a low power, cryogenically compatible platforms for nonlinear microwave photonics, with applications in scalable quantum control and on-chip frequency synthesis.
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.
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.