Detecting faint light from deep space requires an excellent signal-to-noise ratio, as does quantum information processing. For microwave and terahertz frequencies, a simple directional amplifier offering minimal added loss and easy on-chip integration would be a major step forward. This study envisions such an amplifier as two Josephson-junction oscillators plus an on-chip passive circuit, promising 20 dB of gain while adding only ~1 photon s${}^{\ensuremath{-}1}$ Hz${}^{\ensuremath{-}1}$ of noise. This work addresses scale-up in circuit QED and detector research by integrating directional signal routing and amplification, allowing more qubits or pixels per unit area.
Detecting faint light from deep space requires an excellent signal-to-noise ratio, as does quantum information processing. For microwave and terahertz frequencies, a simple directional amplifier offering minimal added loss and easy on-chip integration would be a major step forward. This study envisions such an amplifier as two Josephson-junction oscillators plus an on-chip passive circuit, promising 20 dB of gain while adding only ~1 photon s\ensuremath−1 Hz\ensuremath−1 of noise. This work addresses scale-up in circuit QED and detector research by integrating directional signal routing and amplification, allowing more qubits or pixels per unit area.
We present a way to achieve fully directional, quantum-limited phase-preserving amplification in a four-port, four-mode superconducting Josephson circuit by utilizing interference between six parametric processes that couple all four modes. Full directionality, defined as the reverse isolation surpassing forward gain between the matched input and output ports of the amplifier, ensures its robustness against impedance mismatch that might be present at its output port during applications. Unlike existing directional phase-preserving amplifiers, both the minimal backaction and the quantum-limited added noise of this amplifier remains unaffected by noise incident on its output port. In addition, the matched input and output ports allow direct on-chip integration of these amplifiers with other circuit QED components, facilitating scaling up of superconducting quantum processors.
Low-noise microwave amplifiers are crucial for detecting weak signals in fields such as quantum technology and radio astronomy. However, designing an ideal amplifier is challenging, as it must cover a wide frequency range, add minimal noise, and operate directionally - amplifying signals only in the observer's direction while protecting the source from environmental interference. In this work, we demonstrate that an array of non-linearly coupled Josephson parametric amplifiers (JPAs) can collectively function as a directional, broadband quantum amplifier by harnessing topological effects. By applying a collective four-wave-mixing pump with inhomogeneous amplitudes and linearly increasing phase, we break time-reversal symmetry in the JPA array and stabilize a topological amplification regime where signals are exponentially amplified in one direction and exponentially suppressed in the opposite. We show that compact devices with few sites N∼11−17 can achieve exceptional performance, with gains exceeding 20 dB over a bandwidth ranging from hundreds of MHz to GHz, and reverse isolation suppressing backward noise by more than 30 dB across all frequencies. The device also operates near the quantum noise limit and provides topological protection against up to 15% fabrication disorder, effectively suppressing gain ripples. The amplifier's intrinsic directionality eliminates the need for external isolators, paving the way for fully on-chip, near-ideal superconducting pre-amplifiers.
Nowadays, it is possible to control and measure the quantum state of systems with a few degrees of freedom, whether they are microscopic objects like cold atoms and single photons, or macroscopic objects like superconducting circuits. Such delicate experiments require an interface which bridges the gap of orders of magnitudes in energy between the quantum object and the data acquisition system. This problem is solved by an active device: the amplifier. Although the amplifier is necessary to overcome the noise at the stage of data acquisition, it eventually alters the signal. We have developed an amplifier for microwave signals which adds only the minimum of noise allowed by quantum laws: the equivalent of half a photon of noise referred to the input. Our amplifier is based on a superconducting circuit of Josephson junctions in superconducting resonators. We found a way to make it practical to use by tuning its center frequency over 500 MHz. We are now trying to increase its bandwidth for a given gain using more compact resonators. In this talk, I will show how the amplifier works and also its applications to quantum information processing. This circuit can be used to generate and combine twin microwave photons within an integrated circuit. Finally, I will show that such an amplifier allows real time measurement of the state of a qubit and quantum feedback protocols.
Amplifiers are crucial in every experiment carrying out a very sensitive measurement. However, they always degrade the information by adding noise. Quantum mechanics puts a limit on how small this degradation can be. Theoretically, the minimum noise energy added by a phase-preserving amplifier to the signal it processes amounts at least to half a photon at the signal frequency. In this article, we show that we can build a practical microwave amplifying circuit that fulfills the minimal requirements to reach this quantum limit. The readout of solid-state qubits, and more generally, the measurement of very weak signals in various areas of science, can benefit from this new superconducting device. We also discuss how our circuit can be the basic buiding block for a variety of practical applications such as frequency conversion with and without photon number gain, dynamic cooling and production of entangled signal pairs.
Bringing signals from quantum to classical, from few-photon to many-photon levels for further processing, is a common challenge in rising quantum technologies. These include quantum computing, quantum communication, quantum sensing, radio astronomy, and dark matter searches, typically operating at microwave frequencies and millikelvin temperatures. Superconducting parametric amplifiers, as the first piece in the readout chain, have become a cornerstone of these technologies, since they offer unrivaled noise performance near the quantum-mechanical limit and high gain to surpass the noise of subsequent amplifiers. A notable implementation is the Josephson traveling-wave parametric amplifier (TWPA), which stands out due to its bandwidth of several Gigahertz and high saturation power, often larger than -100 dBm. These key properties come at the cost of complexity in design and fabrication: TWPA metamaterials often contain several thousands of Josephson junctions. Designing high-gain TWPAs involves three major challenges: ensuring impedance-matching, phase-matching of parametric amplification, and suppressing unwanted processes, all achievable through sub-wavelength dispersion engineering. This thesis covers the circuit design and analysis, implementation, and experimental characterization of a dispersion-engineered TWPA based on radio-frequency superconducting interference devices (rf-SQUIDs). It focuses on a detailed investigation of dispersion-engineering techniques and their effects on amplifier performance, particularly through the use of time-domain circuit simulations to analyze the multimode dynamics of the circuit. The experimentally realized device features 18 dB of gain, an instantaneous bandwidth spanning from 2.2 to 6.7 GHz, a system noise of 2.5 quanta, and a saturation power of (−86.5 ± 4.0) dBm. With these characteristics, it is suitable for frequency-multiplexed readout of detector arrays or qubits. Its high saturation power, about 10 dB higher than other reported Josephson-junction-based TWPAs, allows increasing the number of qubits per readout line, or decreasing the intermodulation between frequency-multiplexed qubits, both crucial for scaling up quantum computation.
High-fidelity qubit measurement is a critical element of all quantum computing architectures. In superconducting systems, qubits are typically measured by probing a readout resonator with a weak microwave tone that must be amplified before reaching the room temperature electronics. Superconducting parametric amplifiers have been widely adopted as the first amplifier in the chain, primarily because of their low noise performance, approaching the quantum limit. However, they require isolators and circulators to route signals up the measurement chain and to protect qubits from amplified noise. While these commercial components are wideband and simple to use, their intrinsic loss, size, and magnetic shielding requirements impact overall measurement efficiency and scalability. Here we report a parametric amplifier that achieves both broadband forward amplification and backward isolation in a single, compact, non-magnetic circuit that could be integrated on chip with superconducting qubits. The approach relies on a nonlinear transmission line that supports traveling-wave parametric amplification of forward propagating signals, and isolation via frequency conversion of backward propagating signals. This traveling-wave parametric amplifier and converter has the potential to reduce the readout hardware overhead when scaling up the size of superconducting quantum computers.