Squeezing of the electromagnetic vacuum is an essential metrological technique used to reduce quantum noise in applications spanning gravitational wave detection, biological microscopy, and quantum information science. In superconducting circuits, the resonator-based Josephson-junction parametric amplifiers conventionally used to generate squeezed microwaves are constrained by a narrow bandwidth and low dynamic range. In this work, we develop a dual-pump, broadband Josephson traveling-wave parametric amplifier that combines a phase-sensitive extinction ratio of 56 dB with single-mode squeezing on par with the best resonator-based squeezers. We also demonstrate two-mode squeezing at microwave frequencies with bandwidth in the gigahertz range that is almost two orders of magnitude wider than that of contemporary resonator-based squeezers. Our amplifier is capable of simultaneously creating entangled microwave photon pairs with large frequency separation, with potential applications including high-fidelity qubit readout, quantum illumination and teleportation. 

/pdf/broadband-squeezed-microwaves-and-amplification-with-a-17b84a1k.pdf

Broadband squeezed microwaves and amplification with a Josephson travelling-wave parametric amplifier

We report on the implementation of a near-quantum-limited, traveling-wave parametric amplifier that uses three-wave mixing (3WM). To favor amplification by 3WM, we use superconducting nonlinear asymmetric inductive element (SNAIL) loops, biased with a dc magnetic flux. In addition, we equip the device with dispersion engineering features to create a stopband at the second harmonic of the pump and suppress the propagation of the higher harmonics that otherwise degrade the amplification. With a chain of 440 SNAILs, the amplifier provides up to 20 dB gain and a 3-dB bandwidth of 1 GHz. The added noise by the amplifier is found to be less than one photon.

/pdf/three-wave-mixing-traveling-wave-parametric-amplifier-with-3rqxloe1.pdf

Three-wave mixing traveling-wave parametric amplifier with periodic variation of the circuit parameters

The recently proposed Josephson traveling-wave parametric amplifier (JTWPA) based on a ladder transmission line consisting of radio-frequency superconducting quantum interference devices and exploiting three-wave mixing has great potential in achieving both a gain of 20 dB and a flat bandwidth of at least 4 GHz. To realize this concept in practical amplifiers, we model the advanced JTWPA circuit with periodic modulation of the circuit parameters (engineered dispersion loadings), which allow the basic mixing process, i.e., [Formula: see text], where [Formula: see text], [Formula: see text], and [Formula: see text] are the signal, the pump, and the idler frequencies, respectively, and efficiently suppress propagation of unwanted higher tones, including [Formula: see text], [Formula: see text], [Formula: see text], etc. The engineered dispersion loadings allow achieving a sufficiently wide [Formula: see text] dB-bandwidth from [Formula: see text] to [Formula: see text] GHz combined with a reasonably small ripple ([Formula: see text] dB) in the gain-vs-frequency dependence.

/pdf/numerical-analysis-of-a-three-wave-mixing-josephson-1fnx2kik.pdf

Numerical analysis of a three-wave-mixing Josephson traveling-wave parametric amplifier with engineered dispersion loadings

Quantum correlations are a vital resource in advanced information processing based on quantum phenomena. Remarkably, the vacuum state of a quantum field may act as a key element for the generation of multipartite quantum entanglement. In this work, generation of genuine tripartite entangled state and its control is achieved by the use of the phase difference between two continuous pump tones. Control of the subspaces of the covariance matrix for tripartite bisqueezed state is demonstrated. Furthermore, by optimizing the phase relationships in a three‐tone pumping scheme genuine quadripartite entanglement of a generalized H‐graph state ( H∼$\mathcal {\tilde{H}}$ ‐graph) is explored. This scheme provides a comprehensive control toolbox for the entanglement structure and allows to demonstrate, for first time to the authors' knowledge, genuine quadripartite entanglement of microwave modes. All experimental results are verified with numerical simulations of the nonlinear quantum Langevin equation. It is envisioned that quantum resources facilitated by multi‐pump configurations offer enhanced prospects for quantum data processing using parametric microwave cavities.

/pdf/generation-and-structuring-of-multipartite-entanglement-in-a-315yqhes.pdf

Generation and Structuring of Multipartite Entanglement in a Josephson Parametric System

Broadband squeezer of microwave light

Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising superconducting non-linear asymmetric inductive elements to generate frequency (colour) entangled photons from vacuum fluctuations at a rate of 11 mega entangled bits per second with a potential rate above gigabit per second. The device is operated as a traveling wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we realize the first successfully demonstration of single-mode squeezing in such devices - $2.4\pm0.7$ dB below the zero-point level at half of modulation frequency.

Kirill Petrovnin

Papers

Broadband continuous variable entanglement generation using Kerr-free Josephson metamaterial