Directional Josephson traveling-wave parametric amplifier via non-Hermitian topology

Abstract

Low-noise microwave amplification is crucial for detecting weak signals in quantum technologies and radio astronomy. An ideal device must amplify a broad range of frequencies while adding minimal noise, and be directional, so that it favors the observer's direction while protecting the source from its environment. Current amplifiers do not satisfy all these requirements, severely limiting the scalability of superconducting quantum devices. Here, we demonstrate the feasibility of building a near-ideal quantum amplifier using a homogeneous Josephson junction array and the non-trivial topology of its dynamics. Our design relies on breaking timereversal symmetry via a non-local parametric drive, which induces directional amplification in a way similar to edge states in topological insulators. The system then acquires unprecedented amplifying properties, such as a gain growing exponentially with system size, exponential suppression of back-wards noise, and topological protection against disorder. We show that these features allow a state-of-the-art superconducting device to manifest near-quantum-limited directional amplification with a gain largely surpassing 20 dB and -30 dB of reverse attenuation over a large bandwidth of GHz. This opens the door for integrating near-ideal and compact pre-amplifiers on the same chip as quantum processors.

Non-Hermitian topological phases in traveling-wave parametric amplifiers

“…Actually, the qualitatively similar behavior of signal-to-noise ratio in both topological phases seems to indicate that the neighborhood of critical points is an interesting working point for topological amplifiers. There, the amplifier displays great performance, but in practice this has to be balanced to avoid saturation [46]. These ideas can be immediately implemented with current superconducting circuit technology [46] or with trapped ions.…”

“…There, the amplifier displays great performance, but in practice this has to be balanced to avoid saturation [46]. These ideas can be immediately implemented with current superconducting circuit technology [46] or with trapped ions. From a technological point of view, realizing directional broadband amplification that can be integrated on chip, without bulky and lossy isolators, may help to scale up quantum devices.…”

“…The second line contains single and two-mode parametric terms, g s and g c , respectively. This Hamiltonian can be implemented quite naturally in superconducting circuits [47], without the need of Floquet or reservoir engineering, by just doing four-wave mixing in arrays of Josephson junctions and linear oscillators [46]. There, the combination of Kerr effect and parametric driving can effectively provide the parametric terms present in Eq.…”

“…The phase φ can be controlled, for example, with Floquet engineering techniques. In a forthcoming publication we present details on how to implement our topological TWPA scheme by using Kerr non-linearities in a realistic superconducting setup [46], without the need of Floquet engineering or magnetic fields to break time-reversal symmetry. Finally, the squeezing terms that are required for our scheme, can also be implemented with three-wave mixing terms, as explained in Ref.…”

“…• Finally, we have shown that our model can be implemented with different experimental techniques like Floquet engineering with trapped ions or coupled resonators, or by exploiting non-linear terms in superconducting circuits [46].…”