26 research outputs found
Comparing cavity and ordinary laser cooling within the Lamb-Dicke regime
Cavity-mediated cooling has the potential to become one of the most efficient
techniques to cool molecular species down to very low temperatures. In this
paper we analyse cavity cooling with single-laser driving for relatively large
cavity decay rates kappa and relatively large phonon frequencies nu. It is
shown that cavity cooling and ordinary laser cooling are essentially the same
within the validity range of the Lamb-Dicke approximation. This is done by
deriving a closed set of rate equations and calculating the corresponding
stationary state phonon number and cooling rate. For example, when nu is either
much larger or much smaller than kappa, the minimum stationary state phonon
number scales as kappa^2/16 nu^2 (strong confinement regime) and as kappa / 4
nu (weak confinement regime), respectively.Comment: 12 pages, 8 figures, final version accepted for publicatio
Composite quantum systems and environment-induced heating
In recent years, much attention has been paid to the development of
techniques which transfer trapped particles to very low temperatures. Here we
focus our attention on a heating mechanism which contributes to the finite
temperature limit in laser sideband cooling experiments with trapped ions. It
is emphasized that similar heating processes might be present in a variety of
composite quantum systems whose components couple individually to different
environments. For example, quantum optical heating effects might contribute
significantly to the very high temperatures which occur during the collapse
phase in sonoluminescence experiments. It might even be possible to design
composite quantum systems, like atom-cavity systems, such that they
continuously emit photons even in the absence of external driving.Comment: 4 pages, 1 figur
Driven Spin-Boson Luttinger Liquids
We introduce a lattice model of interacting spins and bosons that leads to
Luttinger-liquid physics, and allows for quantitative tests of the theory of
bosonization by means of trapped-ion or superconducting-circuit experiments. By
using a variational bosonization ansatz, we calculate the power-law decay of
spin and boson correlation functions, and study their dependence on a single
tunable parameter, namely a bosonic driving. For small drivings,
Matrix-Product-States (MPS) numerical methods are shown to be efficient and
validate our ansatz. Conversely, even static MPS become inefficient for
large-driving regimes, such that the experiment can potentially outperform
classical numerics, achieving one of the goals of quantum simulations
Hybrid quantum magnetism in circuit-QED: from spin-photon waves to many-body spectroscopy
We introduce a model of quantum magnetism induced by the non-perturbative
exchange of microwave photons between distant superconducting qubits. By
interconnecting qubits and cavities, we obtain a spin-boson lattice model that
exhibits a quantum phase transition where both qubits and cavities
spontaneously polarise. We present a many-body ansatz that captures this
phenomenon all the way, from a the perturbative dispersive regime where photons
can be traced out, to the non-perturbative ultra-strong coupling regime where
photons must be treated on the same footing as qubits. Our ansatz also
reproduces the low-energy excitations, which are described by hybridised
spin-photon quasiparticles, and can be probed spectroscopically from
transmission experiments in circuit-QED, as shown by simulating a possible
experiment by Matrix-Product-State methods.Comment: closer to published versio
A rate equation approach to cavity mediated laser cooling
The cooling rate for cavity mediated laser cooling scales as the Lamb-Dicke
parameter eta squared. A proper analysis of the cooling process hence needs to
take terms up to eta^2 in the system dynamics into account. In this paper, we
present such an analysis for a standard scenario of cavity mediated laser
cooling with eta << 1. Our results confirm that there are many similarities
between ordinary and cavity mediated laser cooling. However, for a weakly
confined particle inside a strongly coupled cavity, which is the most
interesting case for the cooling of molecules, numerical results indicate that
even more detailed calculations are needed to model the cooling process
accurately.Comment: 15 pages, 10 figures, minor corrections, PRA (in press
The interspersed spin boson lattice model
14 págs,; 4 figs.© 2015, EDP Sciences and Springer. We describe a family of lattice models that support a new class of quantum magnetism characterized by correlated spin and bosonic ordering [Phys. Rev. Lett. 112, 180405 (2014)]. We explore the full phase diagram of the model using Matrix-Product-State methods. Guided by these numerical results, we describe a modified variational ansatz to improve our analytic description of the groundstate at low boson frequencies. Additionally, we introduce an experimental protocol capable of inferring the low-energy excitations of the system by means of Fano scattering spectroscopy. Finally, we discuss the implementation and characterization of this model with current circuit-QED technology.We acknowledge support from Spanish MINECO Project FIS2012- 33022, and CAM regional
research consortium QUITEMAD S2009-ESP-1594.Peer Reviewe
Bose-Hubbard models with photon pairing in circuit-QED
In this work we study a family of bosonic lattice models that combine an
on-site repulsion term with a nearest-neighbor pairing term, Like the original Bose-Hubbard model,
the nearest-neighbor term is responsible for the mobility of bosons and it
competes with the local interaction, inducing two-mode squeezing. However,
unlike a trivial hopping, the counter-rotating terms form pairing cannot be
studied with a simple mean-field theory and does not present a quantum phase
transition in phase space. Instead, we show that there is a cross-over from a
pure insulator to long-range correlations that start up as soon as the two-mode
squeezing is switched on. We also show how this model can be naturally
implemented using coupled microwave resonators and superconducting qubits.Comment: Final version, 19 pages, 9 figure
Rotating wave approximation and entropy
This paper studies composite quantum systems, like atom-cavity systems and
coupled optical resonators, in the absence of external driving by resorting to
methods from quantum field theory. Going beyond the rotating wave
approximation, it is shown that the usually neglected counter-rotating part of
the Hamiltonian relates to the entropy operator and generates an irreversible
time evolution. The vacuum state of the system is shown to evolve into a
generalized coherent state exhibiting entanglement of the modes in which the
counter-rotating terms are expressed. Possible consequences at observational
level in quantum optics experiments are currently under study.Comment: 8 pages, 1 figure, introduction extende