Shaping photons: Quantum information processing with bosonic cQED

Abstract

With its rich dynamics, the quantum harmonic oscillator is an innate platform for understanding real-world quantum systems and could even excel as the heart of a quantum computer. A particularly promising and rapidly advancing platform that harnesses quantum harmonic oscillators for information processing is the bosonic circuit quantum electrodynamics (cQED) system. In this article, we provide perspectives on the progress, challenges, and future directions in building a bosonic cQED quantum computer. We describe the main hardware building blocks and how they facilitate quantum error correction, metrology, and simulation. We conclude with our views of the key challenges that lie on the horizon, as well as scientific and cultural strategies for overcoming them and building a practical quantum computer with bosonic cQED hardware.

Simulating Chemistry on Bosonic Quantum Devices

“…Second, the quantum states of QHOs must be prepared, evolved in time according to a chosen unitary transformation, and measured by controlling with an external system without introducing additional decoherence. Within the cQED architecture, a set of superconducting resonators act as qumodes, and a nonlinear auxiliary circuit is used to perform those three functions (initial preparation, unitary evolution, and measurement). − …”

“…Early resonator prototypes focused on the planar design because of the convenience of fabricating superconducting metal circuits on the same chip that contains the auxiliary circuits with standard lithographic tools . A range of geometries have been introduced since, including 3D resonators that can produce coherence time up to milliseconds by taking advantage of their hollow structure . The coupling to the auxiliary circuit can now be achieved, for example, by introducing a center pin in a cylindrical resonator, while placing the auxiliary circuit next to the resonator …”

“…The transmon is coupled to the qumode resonator by extending its superconducting layers to overlap with the resonator’s electromagnetic field. The interaction between the auxiliary circuits and qumodes can be controlled by detuning the qumode and transmon resonance frequencies or changing the overlap between their electromagnetic fields and make it possible to implement the non-Gaussian operations in cQED . The nonlinearities of the cQED devices underlying the non-Gaussian operations are also an exciting avenue to explore.…”

“…In this paper, we focus on a promising experimental realization of a qumode-based platform that uses circuit quantum electrodynamics (cQED) . In this case, superconducting resonators serve as qumodes, with the interactions between resonators controlled via an auxiliary superconducting circuit. − Other hardware approaches to bosonic quantum computing include arrays of trapped ions, , optical modes, or mechanical resonators …”

On-demand transposition across light-matter interaction regimes in bosonic cQED

“…Owing to the rapid advances in cQED hardware, it is now possible to build long-lived cavities and harness their rich dynamics through the manipulation of nonlinear elements such as transmons. This type of bosonic cQED architectures employs these continuous variable modes for quantum information processing 8 , 9 . It provides an ideal playground for exploring the qualitatively distinct behaviours of light-matter interactions, and a valuable platform for quantum error correction 10 – 12 , analogue simulations 13 , 14 and metrology 15 , and even for the long-term goal of engineering a universal quantum computer 9 .…”