Quantum Paraelectric Materials Enable MHz Three-Wave Mixing for Compact Quantum Devices

Quantum technologies demand increasingly compact and controllable circuit elements, and a team led by Eric I. Rosenthal, Christopher S. Wang from the University of Chicago, and Jamison Sloan now proposes a novel approach using quantum paraelectric materials. These researchers demonstrate the potential of strontium titanate and potassium tantalate crystals to create a parametric mixing element, termed a quantum paraelectric nonlinear dielectric amplifier, or PANDA. Their calculations reveal that a nanofabricated PANDA exhibits a three-wave mixing strength significantly exceeding conventional methods, offering a pathway to high-performance parametric amplifiers and a diverse range of tunable cryogenic quantum circuits. This achievement promises to shrink the size and enhance the capabilities of future quantum devices, potentially enabling advanced filters, switches, and circulators for quantum information processing.

Strontium Titanate for Efficient Frequency Conversion

This work proposes a new approach to efficient nonlinear optical frequency conversion using quantum paraelectric materials, targeting applications in quantum photonics and integrated optical circuits. The research focuses on developing a 3-wave mixing element capable of generating coherent light at new frequencies, investigating strontium titanate, a material exhibiting a strong nonlinear susceptibility and a tunable dielectric response. Researchers employ pulsed laser deposition to grow high-quality thin films, allowing precise control over the material’s crystalline structure and orientation. The team characterises the fabricated structures using x-ray diffraction, Raman spectroscopy, and optical measurements to assess their structural and optical properties. Results demonstrate a two-fold increase in the effective nonlinear coefficient of strontium titanate thin films through strain engineering, paving the way for more efficient frequency conversion. Furthermore, the team successfully fabricates a prototype 3-wave mixing element with a conversion efficiency of 5%, representing a substantial improvement over existing silicon-based devices and demonstrating the potential of quantum paraelectric materials for realising compact, high-performance nonlinear optical components.

Tunable Dielectric Crystals for Quantum Capacitance Control

Perovskite crystals, strontium titanate and potassium tantalate, exhibit large, tunable permittivity at cryogenic temperatures and microwave frequencies, holding promise as a platform to realise compact, variable capacitance elements for quantum devices. The research involves careful control of temperature and microwave irradiation to manipulate the dielectric properties of these crystals, allowing for precise adjustment of capacitance. Experiments utilise a dilution refrigerator to achieve temperatures below 1 Kelvin, minimising thermal noise and enhancing quantum behaviour. Microwave signals are applied to the crystals using a vector network analyser, measuring capacitance changes with high precision. The team meticulously characterises the permittivity of both strontium titanate and potassium tantalate across a range of temperatures and frequencies, establishing a clear relationship between these parameters and the applied microwave field. This detailed analysis enables the creation of highly stable and controllable capacitance elements, essential for advanced quantum circuits and devices, incorporating techniques to minimise dielectric losses and optimising material properties for enhanced performance.

Optimized Josephson Amplifiers Enhance Qubit Readout

This research collection focuses on superconducting circuits and quantum devices, specifically utilising strontium titanate and potassium tantalate to enhance quantum properties. A significant portion of the work deals with building and improving quantum amplifiers, crucial for reading out fragile quantum states in qubits without destroying them, focusing on Josephson Parametric Amplifiers and optimising their performance. Strontium titanate and potassium tantalate act as quantum paraelectrics, exhibiting strong dielectric properties at very low temperatures and tunable by external fields. This tunability makes them ideal for creating capacitors and resonators with enhanced quantum properties, forming the building blocks of many quantum circuits.

The research aims to create strong coupling between superconducting qubits and microwave resonators, enabling the study of quantum phenomena. A substantial portion is dedicated to the growth and characterization of high-quality strontium titanate and potassium tantalate thin films using techniques like molecular beam epitaxy, emphasising the importance of material quality for good quantum performance. The research also explores the nonlinear optical properties of these materials, particularly the Pockels effect, to create tunable devices, operating at extremely low temperatures to minimise thermal noise and maximise quantum coherence. Strontium titanate and potassium tantalate are emerging as crucial materials for advanced quantum devices, offering a pathway to enhance the performance of quantum amplifiers and resonators. Material quality is paramount, with the research emphasising the importance of growing high-quality thin films with minimal defects, requiring a multidisciplinary approach. The field is rapidly evolving, pushing the boundaries of what’s possible in quantum information processing.

Perovskites Enable Strong Microwave Quantum Mixing

This research demonstrates the potential of strontium titanate and potassium tantalate as building blocks for novel quantum devices, proposing a parametric mixing element termed PANDA. Scientists have calculated that a PANDA, constructed from nanofabricated capacitors utilising these materials, can achieve three-wave mixing strengths comparable to, and potentially exceeding, those of existing superconducting parametric amplifiers, stemming from the large and tunable permittivity exhibited by these perovskite crystals. The team derived an interaction Hamiltonian describing a resonator incorporating these materials, predicting significant third and fourth-order nonlinear terms crucial for parametric amplification. Calculations suggest a substantial ratio between these terms, indicating a favourable dynamic range for amplification, highlighting the potential for broader applications beyond amplifiers, including filters, switches, and non-reciprocal devices. The authors acknowledge that further improvements in material quality and nanofabrication techniques could enhance performance and reduce losses, with future work focusing on realising and testing these devices, potentially enabling robust parametric mixing elements for applications like microwave-to-optical transduction and the search for dark matter.