We study the phenomena of topological amplification in one-dimensional traveling-wave parametric amplifiers. We find two phases of topological amplification, both with directional transportand exponential gain with the number of sites, and one of them featuring squeezing. We also find a topologically trivial phase with zero-energy modes which produces amplification but lacks topological protection. We characterize the resilience to disorder of the different phases, their stability, gain and noise-to-signal ratio. Finally, we discuss their experimental implementation with state-of-the-art techniques.
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 whileadding 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 time-reversal 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.
We show how a pair of superconducting qubits coupled to a microwave cavity mode can be used to engineer a single-atom laser that emits light into a non-classical state. Our scheme relieson the dressing of the qubit-field coupling by periodic modulations of the qubit energy. In the dressed basis, the radiative decay of the first qubit becomes an effective incoherent pumping mechanism that injects energy into the system, hence turning dissipation to our advantage. A second, auxiliary qubit is used to shape the decay within the cavity, in such a way that lasing occurs in a squeezed basis of the cavity mode. We characterize the system both by mean-field theory and exact calculations. Our work may find applications in the generation of squeezing and entanglement in circuit QED, as well as in the study of dissipative many-body phase transitions.
Based on a circuit QED qubit-cavity array a source of two-mode entangled
microwave radiation is designed. Our scheme is rooted in the combination of
external driving, collective phenomenaand dissipation. On top of that the
reflexion symmetry is broken via external driving permitting the appearance of
chiral emission. Our findings go beyond the applications and are relevant for
fundamental physics, since we show how to implement quantum lattice models
exhibiting criticality driven by dissipation.