7,241 research outputs found
Canonical circuit quantization with linear nonreciprocal devices
Nonreciprocal devices effectively mimic the breaking of time-reversal
symmetry for the subspace of dynamical variables that they couple, and can be
used to create chiral information processing networks. We study the systematic
inclusion of ideal gyrators and circulators into Lagrangian and Hamiltonian
descriptions of lumped-element electrical networks. The proposed theory is of
wide applicability in general nonreciprocal networks on the quantum regime. We
apply it to pedagogical and pathological examples of circuits containing
Josephson junctions and ideal nonreciprocal elements described by admittance
matrices, and compare it with the more involved treatment of circuits based on
nonreciprocal devices characterized by impedance or scattering matrices.
Finally, we discuss the dual quantization of circuits containing phase-slip
junctions and nonreciprocal devices.Comment: 12 pages, 4 figures; changes made to match the accepted version in
PR
Ensemble Quantum Computation with atoms in periodic potentials
We show how to perform universal quantum computation with atoms confined in
optical lattices which works both in the presence of defects and without
individual addressing. The method is based on using the defects in the lattice,
wherever they are, both to ``mark'' different copies on which ensemble quantum
computation is carried out and to define pointer atoms which perform the
quantum gates. We also show how to overcome the problem of scalability on this
system
Quantum Memristors
Technology based on memristors, resistors with memory whose resistance
depends on the history of the crossing charges, has lately enhanced the
classical paradigm of computation with neuromorphic architectures. However, in
contrast to the known quantized models of passive circuit elements, such as
inductors, capacitors or resistors, the design and realization of a quantum
memristor is still missing. Here, we introduce the concept of a quantum
memristor as a quantum dissipative device, whose decoherence mechanism is
controlled by a continuous-measurement feedback scheme, which accounts for the
memory. Indeed, we provide numerical simulations showing that memory effects
actually persist in the quantum regime. Our quantization method, specifically
designed for superconducting circuits, may be extended to other quantum
platforms, allowing for memristor-type constructions in different quantum
technologies. The proposed quantum memristor is then a building block for
neuromorphic quantum computation and quantum simulations of non-Markovian
systems
Deep Strong Coupling Regime of the Jaynes-Cummings model
We study the quantum dynamics of a two-level system interacting with a
quantized harmonic oscillator in the deep strong coupling regime (DSC) of the
Jaynes-Cummings model, that is, when the coupling strength g is comparable or
larger than the oscillator frequency w (g/w > 1). In this case, the
rotating-wave approximation cannot be applied or treated perturbatively in
general. We propose an intuitive and predictive physical frame to describe the
DSC regime where photon number wavepackets bounce back and forth along parity
chains of the Hilbert space, while producing collapse and revivals of the
initial population. We exemplify our physical frame with numerical and
analytical considerations in the qubit population, photon statistics, and
Wigner phase space.Comment: Published version, note change of title: DSC regime of the JC mode
Circuit Quantum Electrodynamics with a Superconducting Quantum Point Contact
We consider a superconducting quantum point contact in a circuit quantum
electrodynamics setup. We study three different configurations, attainable with
current technology, where a quantum point contact is coupled galvanically to a
coplanar waveguide resonator. Furthermore, we demonstrate that the strong and
ultrastrong coupling regimes can be achieved with realistic parameters,
allowing the coherent exchange between a superconducting quantum point contact
and a quantized intracavity field.Comment: 5 pages, 4 figures. Updated version, accepted for publication as a
Rapid Communication in Physical Review
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