Phase preserving amplification near the quantum limit with a Josephson Ring Modulator (0912.3407v1)

Abstract: Recent progress in solid state quantum information processing has stimulated the search for ultra-low-noise amplifiers and frequency converters in the microwave frequency range, which could attain the ultimate limit imposed by quantum mechanics. In this article, we report the first realization of an intrinsically phase-preserving, non-degenerate superconducting parametric amplifier, a so far missing component. It is based on the Josephson ring modulator, which consists of four junctions in a Wheatstone bridge configuration. The device symmetry greatly enhances the purity of the amplification process and simplifies both its operation and analysis. The measured characteristics of the amplifier in terms of gain and bandwidth are in good agreement with analytical predictions. Using a newly developed noise source, we also show that our device operates within a factor of three of the quantum limit. This development opens new applications in the area of quantum analog signal processing.

• The paper’s main contribution is the design and experimental validation of a Josephson Parametric Converter that achieves >40 dB gain while operating within three times the quantum noise limit.
• It employs a non-degenerate Wheatstone bridge of four Josephson junctions to enable efficient three-wave mixing for phase-preserving amplification.
• The study introduces a noise calibration method using a mesoscopic resistor, directly comparing performance to the quantum limit and advancing quantum detection capabilities.

Phase Preserving Amplification Near the Quantum Limit with a Josephson Ring Modulator

The paper "Phase preserving amplification near the quantum limit with a Josephson Ring Modulator" presents significant advancements in the development of superconducting parametric amplifiers, specifically focusing on a device that operates near the quantum limit for noise. The work introduces the Josephson Parametric Converter (JPC), an intrinsically phase-preserving amplifier that is a crucial component for quantum analog signal processing in solid-state quantum information systems.

Summary of Technical Contributions

This report details the realization of a non-degenerate superconducting parametric amplifier using a Josephson ring modulator, configured in a Wheatstone bridge of four Josephson junctions. This configuration enhances amplification purity and facilitates operational simplicity. The authors highlight that the device's characteristics of gain and bandwidth align well with analytical predictions, showcasing its operational efficiency.

A key contribution of the paper is the quantification of the amplifier's performance at approximately a factor of three from the quantum limit—a remarkable proximity achieved through the novel use of a noise source. The amplifier operates with gains exceeding 40 dB and distinguishes between signal and idler modes, a defining feature enabling efficient frequency conversion.

Device Architecture and Operation

The JPC comprises two superconducting resonators which interface with the differential modes of the Josephson ring modulator. The innovative design extends to isolating signal and idler modes both spatially and temporally, making the device notable for applications requiring phase preservation, where the information is often embedded in both quadratures.

The non-linear inductance of the Josephson ring modulator is the vital element, facilitating efficient three-wave mixing required for the amplifier's operation. The paper introduces mathematical models that describe the input-output relations and noise properties of the JPC in the quantum regime, with the device functioning as either a phase-preserving amplifier or a unity photon gain frequency converter depending on pump frequency configurations.

Experimental Results

Experimental validation of the JPC reveals excellent agreement with theoretical models up to 40 dB power gain. This is structurally influenced by the non-linear coupling inherent in the XYZ modes of the Josephson ring modulator. The gain-bandwidth relationship suggested by the theory was proven robust, further advancing the model's reliability.

Noise analysis was conducted using a mesoscopic resistor in the hot-electron regime to serve as a noise source. This novel approach to calibration and measurement permits a direct comparison of the amplifier's noise performance against the quantum limit. The paper reveals the amplifier's added noise power measures threefold the theoretical quantum minimum, as estimated through the system's design parameters.

Implications and Future Developments

This work has substantial implications for the future of quantum electronics, particularly in advancing detection sensitivity for low-power microwave applications. The JPC's design and performance metrics suggest the possibility of enhancing dispersive readout mechanisms essential for solid-state qubit measurements with significantly reduced irradiation.

Future developments could focus on optimizing resonator coupling to enhance bandwidth without compromising gain, potentially driving the operational noise of such amplifiers even closer to the quantum limit. Moreover, the novel architecture offers avenues to explore entangled microwave signal generation, potentially expanding applications in quantum information processing.

This research provides a well-founded stepping stone towards the practical realization of quantum-limited amplifiers, positioned to have a transformative impact on emerging quantum technologies.