25 research outputs found
Cavity-assisted quantum bath engineering
We demonstrate quantum bath engineering for a superconducting artificial atom
coupled to a microwave cavity. By tailoring the spectrum of microwave photon
shot noise in the cavity, we create a dissipative environment that autonomously
relaxes the atom to an arbitrarily specified coherent superposition of the
ground and excited states. In the presence of background thermal excitations,
this mechanism increases the state purity and effectively cools the dressed
atom state to a low temperature
Single-photon Resolved Cross-Kerr Interaction for Autonomous Stabilization of Photon-number States
Quantum states can be stabilized in the presence of intrinsic and
environmental losses by either applying active feedback conditioned on an
ancillary system or through reservoir engineering. Reservoir engineering
maintains a desired quantum state through a combination of drives and designed
entropy evacuation. We propose and implement a quantum reservoir engineering
protocol that stabilizes Fock states in a microwave cavity. This protocol is
realized with a circuit quantum electrodynamics platform where a Josephson
junction provides direct, nonlinear coupling between two superconducting
waveguide cavities. The nonlinear coupling results in a single photon resolved
cross-Kerr effect between the two cavities enabling a photon number dependent
coupling to a lossy environment. The quantum state of the microwave cavity is
discussed in terms of a net polarization and is analyzed by a measurement of
its steady state Wigner function.Comment: 8 pages, 6 figure
Stabilizing a Bell state of two superconducting qubits by dissipation engineering
We propose a dissipation engineering scheme that prepares and protects a
maximally entangled state of a pair of superconducting qubits. This is done by
off-resonantly coupling the two qubits to a low-Q cavity mode playing the role
of a dissipative reservoir. We engineer this coupling by applying six
continuous-wave microwave drives with appropriate frequencies. The two qubits
need not be identical. We show that our approach does not require any
fine-tuning of the parameters and requires only that certain ratios between
them be large. With currently achievable coherence times, simulations indicate
that a Bell state can be maintained over arbitrary long times with fidelities
above 94%. Such performance leads to a significant violation of Bell's
inequality (CHSH correlation larger than 2.6) for arbitrary long times.Comment: 5 pages, 4 figure
Stabilizing entanglement autonomously between two superconducting qubits
Quantum error-correction codes would protect an arbitrary state of a
multi-qubit register against decoherence-induced errors, but their
implementation is an outstanding challenge for the development of large-scale
quantum computers. A first step is to stabilize a non-equilibrium state of a
simple quantum system such as a qubit or a cavity mode in the presence of
decoherence. Several groups have recently accomplished this goal using
measurement-based feedback schemes. A next step is to prepare and stabilize a
state of a composite system. Here we demonstrate the stabilization of an
entangled Bell state of a quantum register of two superconducting qubits for an
arbitrary time. Our result is achieved by an autonomous feedback scheme which
combines continuous drives along with a specifically engineered coupling
between the two-qubit register and a dissipative reservoir. Similar autonomous
feedback techniques have recently been used for qubit reset and the
stabilization of a single qubit state, as well as for creating and stabilizing
states of multipartite quantum systems. Unlike conventional, measurement-based
schemes, an autonomous approach counter-intuitively uses engineered dissipation
to fight decoherence, obviating the need for a complicated external feedback
loop to correct errors, simplifying implementation. Instead the feedback loop
is built into the Hamiltonian such that the steady state of the system in the
presence of drives and dissipation is a Bell state, an essential building-block
state for quantum information processing. Such autonomous schemes, broadly
applicable to a variety of physical systems as demonstrated by a concurrent
publication with trapped ion qubits, will be an essential tool for the
implementation of quantum-error correction.Comment: 39 pages, 7 figure
The magnetic genome of two-dimensional van der Waals materials
Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research