Bath engineering, which utilizes coupling to lossy modes in a quantum system to generate nontrivial steady states, is a tantalizing alternative to gate- and measurement-based quantum science. Here, we demonstrate dissipative stabilization of entanglement between two superconducting transmon qubits in a symmetry-selective manner. We utilize the engineered symmetries of the dissipative environment to stabilize a target Bell state; we further demonstrate suppression of the Bell state of opposite symmetry due to parity selection rules. This implementation is resource efficient, achieves a steady-state fidelity F=0.70, and is scalable to multiple qubits.
Superconducting quantum circuits provide a promising avenue for scalable quantum computation and simulation. Their chief advantage is that, unlike physical atoms or electrons, these ``artificial atoms'' can be designed with nearly-arbitrarily large coupling to one another and to their electromagnetic environment. This strong coupling allows for fast quantum bit (qubit) operations, and for efficient readout. However, strong coupling comes at a price: a qubit that is strongly coupled to its environment is also strongly susceptible to losses and dissipation, as coherent information leaks from the quantum system under study into inaccessible ``bath'' modes. Extensive work in the field is dedicated to engineering away these losses to the extent possible, and to using error correction to undo the effects of losses that are unavoidable.This dissertation explores an alternate approach to dissipation: we study avenues by which dissipation itself can be used to generate, rather than destroy, quantum resources. We do so specifically in the context of quantum entanglement, one of the most important and most counter-intuitive aspects of quantum mechanics. Entanglement generation and stabilization is critical to most non-trivial implementations of quantum computing and quantum simulation, as it is the property that distinguishes a multi-qubit quantum system from a string of classical bits. The ability to harness dissipation to generate, purify, and stabilize entanglement is therefore highly desirable.We begin with an overview of quantum dissipation and measurement, followed by an introduction to entanglement and to the superconducting quantum information architecture. We then discuss three sets of experiments that highlight and explore the powerful uses of dissipation in quantum systems. First, we use an entangling measurement to probabilistically generate entanglement between two qubits separated by more than one meter of ordinary cable. This represents the first achievement of remote entanglement in a superconducting qubit system, which will be a critical capability as quantum computers and simulators scale. We then use a nearly-quantum limited amplifier to unravel individual quantum trajectories of the system under that entangling measurement, performing the first systematic exploration of entangled trajectories in any physical implementation. We finally demonstrate deterministic entanglement by engineering a lossy quantum environment to efficiently generate and stabilize entangled states with both frequency and symmetry selectivity. These experiments provide evidence that explicitly building dissipation into an engineered quantum system can enable, rather than hinder, the study of fundamental quantum mechanics and complex many-body Hamiltonians.
We present how to dissipatively prepare genuinely multipartite-entangled steady states with mutually independent local reservoirs by harnessing an Abelian strong symmetry and temporal bath correlations. In interacting Ising chains, we demonstrate that, for a broad class of system-environment couplings, flat baths exponentially erase Ising-axis correlations. Structured baths overcome this obstruction by converting temporal bath correlations into classical spatial correlations. Strong symmetry then promotes these correlations to the quantum domain, enabling global multipartite entanglement. Within weak-coupling theory, we obtain exact steady states despite the generator's nonquadratic nature: strong symmetry reduces their construction to a classical problem for arbitrary Ising couplings. This reduction reveals an exact connection between classical distinguishability and entanglement. We then show how to engineer the bath spectrum to increase the correlation length and enable the preparation of GHZ-like states from separable initial conditions. We test the mechanism beyond the analytical regime using exact Markovian embeddings and tensor-network simulations. Our approach is particularly suited to superconducting and trapped-ion platforms, and we propose a concrete implementation for the latter using sympathetically cooled motional modes.
Engineered dissipation provides a powerful route to controlling and stabilizing quantum states in open systems. Superconducting circuits are particularly suited to this approach due to their tunable coupling to dissipative environments. Here we realize programmable local reservoirs for superconducting qubits through parametrically driven coupling to readout resonators, creating energy-selective incoherent pump and loss. Using coupled superconducting qubits, we autonomously stabilize entangled single-excitation states with fidelity up to 90.8%. We probe the stabilization dynamics under varying initial conditions and bath parameters, and implement robust classical shadow estimation for accurate and scalable state characterization. Finally, we numerically study a configuration where the engineered pump and loss share a common dissipative mode, leading to reservoir-mediated interference and classically correlated steady states. Our results demonstrate a scalable and hardware-efficient framework for dissipative preparation and control of correlated many-body states in superconducting circuits.