162 research outputs found
Anisotropic quantum emitter interactions in two-dimensional photonic-crystal baths
Quantum emitters interacting with two-dimensional photonic-crystal baths
experience strong and anisotropic collective dissipation when they are
spectrally tuned to 2D Van-Hove singularities. In this work, we show how to
turn this dissipation into coherent dipole-dipole interactions with tuneable
range by breaking the lattice degeneracy at the Van-Hove point with a
superlattice geometry. Using a coupled-mode description, we show that the
origin of these interactions stems from the emergence of a qubit-photon bound
state which inherits the anisotropic properties of the original dissipation,
and whose spatial decay can be tuned via the superlattice parameters or the
detuning of the optical transition respect to the band-edges. Within that
picture, we also calculate the emitter induced dynamics in an exact manner,
bounding the parameter regimes where the dynamics lies within a Markovian
description. As an application, we develop a four-qubit entanglement protocol
exploiting the shape of the interactions. Finally, we provide a
proof-of-principle example of a photonic crystal where such interactions can be
obtained.Comment: 12 pages, 8 figure
Purely Long-Range Coherent Interactions in Two-Dimensional Structured Baths
In this work we study the quantum dynamics emerging when quantum emitters
exchange excitations with a two-dimensional bosonic bath with hexagonal
symmetry. We show that a single quantum emitter spectrally tuned to the middle
of the band relaxes following a logarithmic law in time due to the existence of
a singular point with vanishing density of states, i.e., the Dirac point.
Moreover, when several emitters are coupled to the bath at that frequency,
long-range coherent interactions between them appear which decay inversely
proportional to their distance without exponential attenuation. We analyze both
the finite and infinite system situation using both perturbative and
non-perturbative methods.Comment: 18 pages, 7 figures. Text restructured. Extended discussion on
experimental consideration
Non-Markovian Quantum Optics with Three-Dimensional State-Dependent Optical Lattices
Quantum emitters coupled to structured photonic reservoirs experience
unconventional individual and collective dynamics emerging from the interplay
between dimensionality and non-trivial photon energy dispersions. In this work,
we systematically study several paradigmatic three dimensional structured baths
with qualitative differences in their bath spectral density. We discover
non-Markovian individual and collective effects absent in simplified
descriptions, such as perfect subradiant states or long-range anisotropic
interactions. Furthermore, we show how to implement these models using only
cold atoms in state-dependent optical lattices and show how this unconventional
dynamics can be observed with these systems.Comment: 39 pages, 17 figures. Accepted versio
Heralded multiphoton states with coherent spin interactions in waveguide QED
WaveguideQEDoffers the possibility of generating strong coherent atomic
interactions either through appropriate atomic configurations in the
dissipative regime or in the bandgap regime. In this work, we show how to
harness these interactions in order to herald the generation of highly
entangled atomic states, which afterwards can be mapped to generate single mode
multi-photonic states with high fidelities.Weintroduce two protocols for the
preparation of the atomic states, we discuss their performance and compare them
to previous proposals. In particular, we show that one of them reaches high
probability of success for systems with many atoms but low Purcell factors
Quantum Spin Dynamics with Pairwise-Tunable, Long-Range Interactions
We present a platform for the simulation of quantum magnetism with full
control of interactions between pairs of spins at arbitrary distances in one-
and two-dimensional lattices. In our scheme, two internal atomic states
represent a pseudo-spin for atoms trapped within a photonic crystal waveguide
(PCW). With the atomic transition frequency aligned inside a band gap of the
PCW, virtual photons mediate coherent spin-spin interactions between lattice
sites. To obtain full control of interaction coefficients at arbitrary
atom-atom separations, ground-state energy shifts are introduced as a function
of distance across the PCW. In conjunction with auxiliary pump fields,
spin-exchange versus atom-atom separation can be engineered with arbitrary
magnitude and phase, and arranged to introduce non-trivial Berry phases in the
spin lattice, thus opening new avenues for realizing novel topological spin
models. We illustrate the broad applicability of our scheme by explicit
construction for several well known spin models.Comment: 18 pages, 10 figure
Deterministic generation of arbitrary photonic states assisted by dissipation
A scheme to utilize atom-like emitters coupled to nanophotonic waveguides is
proposed for the generation of many-body entangled states and for the
reversible mapping of these states of matter to photonic states of an optical
pulse in the waveguide. Our protocol makes use of decoherence-free subspaces
(DFS) for the atomic emitters with coherent evolution within the DFS enforced
by strong dissipative coupling to the waveguide. By switching from subradiant
to superradiant states, entangled atomic states are mapped to photonic states
with high fidelity. An implementation using ultracold atoms coupled to a
photonic crystal waveguide is discussed.Comment: 15 pages, 4 figure
Universal quantum computation in waveguide QED using decoherence free subspaces
The interaction of quantum emitters with one-dimensional photon-like reservoirs induces strong and long-range dissipative couplings that give rise to the emergence of the so-called decoherence free subspaces (DFSs) which are decoupled from dissipation. When introducing weak perturbations on the emitters, e.g., driving, the strong collective dissipation enforces an effective coherent evolution within the DFS. In this work, we show explicitly how by introducing single-site resolved drivings, we can use the effective dynamics within the DFS to design a universal set of one and two-qubit gates within the DFS of an ensemble of two-level atom-like systems. Using Liouvillian perturbation theory we calculate the scaling with the relevant figures of merit of the systems, such as the Purcell factor and imperfect control of the drivings. Finally, we compare our results with previous proposals using atomic Λ systems in leaky cavities
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