Search

Abstract Quantum information processors benefit from high clock frequencies to fully harness quantum advantages before they are lost to decoherence. All-optical systems offer unique benefits due to their inherent 100-THz carrier frequency, enabling the development of THz-clock frequency processors. However, the bandwidth of quantum light sources and measurement devices has been limited to the MHz range, with nonclassical state generation rates in the kHz range. In this study, we demonstrated broadband generation and quantum tomography of non-Gaussian states using an optical parametric amplifier (OPA) as a squeezed light source and an optical phase-sensitive amplifier (PSA). Our system includes a 6-THz squeezed-light source, a 6-THz PSA, and a 66-GHz homodyne detector. We successfully generated non-Gaussian states at a 0.9 MHz rate with sub-nanosecond wave packets using a continuous-wave laser. The performance is currently limited by the jitter of superconducting detectors, restricting the usable bandwidth to 1 GHz. Our technique extends the bandwidth to GHz, potentially increasing non-Gaussian state generation rates for practical optical quantum processors using OPAs.

Abstract Practical quantum computing requires robust encoding of logical qubits in physical systems to protect fragile quantum information. Currently, the lack of scalability limits the logical encoding in most physical systems, and thus the high scalability of propagating light can be a game changer. However, propagating light also has difficulty in logical encoding due to weak nonlinearity. Here, we propose a synthesizer that encodes Gottesman-Kitaev-Preskill (GKP) qubits in propagating light by exploiting the nonlinearity of photon detectors. This synthesizer is based on an approach what we call Gaussian breeding, leading to the following four advantages: (i) systematic and rigorous synthesis of arbitrary GKP qubits, (ii) use of minimal resources, (iii) high fidelity and high success probability, and (iv) robustness against loss. There has been no protocol that incorporates all these advantages, and thus the proposed synthesizer excels in both performance and feasibility. By employing our method, one can generate GKP qubits using a few to several squeezed light sources, beam splitters and photon detectors.

Enhancing light-matter interaction at gigahertz rates has so far been achieved by structural modification of materials, but does not allow the behaviour to be switched on-demand. Here, an alternative method using pulsed light is presented that provides improved control.