176 research outputs found
Circuit QED and engineering charge based superconducting qubits
The last two decades have seen tremendous advances in our ability to generate
and manipulate quantum coherence in mesoscopic superconducting circuits. These
advances have opened up the study of quantum optics of microwave photons in
superconducting circuits as well as providing important hardware for the
manipulation of quantum information. Focusing primarily on charge-based qubits,
we provide a brief overview of these developments and discuss the present state
of the art. We also survey the remarkable progress that has been made in
realizing circuit quantum electrodynamics (QED) in which superconducting
artificial atoms are strongly coupled to individual microwave photons.Comment: Proceedings of Nobel Symposium 141: Qubits for Future Quantum
Informatio
Dissipative Pairing Interactions: Quantum Instabilities, Topological Light, and Volume-Law Entanglement
We analyze an unusual class of bosonic dynamical instabilities that arise
from dissipative (or non-Hermitian) pairing interactions. We show that,
surprisingly, a completely stable dissipative pairing interaction can be
combined with simple hopping or beam-splitter interactions (also stable) to
generate instabilities. Further, we find that the dissipative steady state in
such a situation remains completely pure up until the instability threshold (in
clear distinction from standard parametric instabilities). These
pairing-induced instabilities also exhibit an extremely pronounced sensitivity
to wavefunction localization. This provides a simple yet powerful method for
selectively populating and entangling edge modes of photonic (or more general
bosonic) lattices having a topological bandstructure. The underlying
dissipative pairing interaction is experimentally resource-friendly, requiring
the addition of a single additional localized interaction to an existing
lattice, and is compatible with a number of existing platforms, including
superconducting circuits
Propagating Quantum Microwaves: Towards Applications in Communication and Sensing
The field of propagating quantum microwaves has started to receive
considerable attention in the past few years. Motivated at first by the lack of
an efficient microwave-to-optical platform that could solve the issue of secure
communication between remote superconducting chips, current efforts are
starting to reach other areas, from quantum communications to sensing. Here, we
attempt at giving a state-of-the-art view of the two, pointing at some of the
technical and theoretical challenges we need to address, and while providing
some novel ideas and directions for future research. Hence, the goal of this
paper is to provide a bigger picture, and -- we hope -- to inspire new ideas in
quantum communications and sensing: from open-air microwave quantum key
distribution to direct detection of dark matter, we expect that the recent
efforts and results in quantum microwaves will soon attract a wider audience,
not only in the academic community, but also in an industrial environment
The SLH framework for modeling quantum input-output networks
Many emerging quantum technologies demand precise engineering and control
over networks consisting of quantum mechanical degrees of freedom connected by
propagating electromagnetic fields, or quantum input-output networks. Here we
review recent progress in theory and experiment related to such quantum
input-output networks, with a focus on the SLH framework, a powerful modeling
framework for networked quantum systems that is naturally endowed with
properties such as modularity and hierarchy. We begin by explaining the
physical approximations required to represent any individual node of a network,
eg. atoms in cavity or a mechanical oscillator, and its coupling to quantum
fields by an operator triple . Then we explain how these nodes can be
composed into a network with arbitrary connectivity, including coherent
feedback channels, using algebraic rules, and how to derive the dynamics of
network components and output fields. The second part of the review discusses
several extensions to the basic SLH framework that expand its modeling
capabilities, and the prospects for modeling integrated implementations of
quantum input-output networks. In addition to summarizing major results and
recent literature, we discuss the potential applications and limitations of the
SLH framework and quantum input-output networks, with the intention of
providing context to a reader unfamiliar with the field.Comment: 60 pages, 14 figures. We are still interested in receiving
correction
Three-wave Mixing in Superconducting Circuits: Stabilizing Cats with SNAILs
Three-wave mixing, by which a photon splits into two correlated photons and vice versa, is a powerful quantum process with many applications in fundamental quantum mechanics experiments and quantum information processing. However, in superconducting circuits, the predominant form of nonlinearity provided by a Josephson junction is only of even order, and thus symmetry forbids three-wave mixing. This Kerr nonlinearity is useful in its own right for engineering quantum operations, but it is accompanied by unavoidable frequency shifts that become especially problematic as the number of interacting electromagnetic modes, and therefore frequency crowding, increases. How then can we endow superconducting devices with the necessary nonlinearity to perform three-wave mixing? In this thesis, we introduce a simple and compact way to add three-wave-mixing capabilities to a superconducting circuit: the superconducting nonlinear inductive element (SNAIL). Additionally, we optimize these devices for quantum-coherent three-wave mixing applications. The many orders of magnitude over which circuit nonlinearities may be designed allow a rich space for different behaviors. We focus on three-wave mixing for single-mode squeezing in two distinct contexts: quantum-noise-limited parametric amplification, and protection of quantum information in a Schrödinger cat qubit. The former showcases the capability to design three-wave-mixing processes free of residual Kerr nonlinearity; the latter explicitly includes Kerr nonlinearity to protect quantum information from decoherence and quickly manipulate it. Both applications indicate the importance of three-wave mixing in quantum information contexts and for the exploration of fundamental quantum effects
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