29,993 research outputs found
PT-symmetric laser-absorber
In a recent work, Y.D. Chong et al. [Phys. Rev. Lett. {\bf 105}, 053901
(2010)] proposed the idea of a coherent perfect absorber (CPA) as the
time-reversed counterpart of a laser, in which a purely incoming radiation
pattern is completely absorbed by a lossy medium. The optical medium that
realizes CPA is obtained by reversing the gain with absorption, and thus it
generally differs from the lasing medium. Here it is shown that a laser with an
optical medium that satisfies the parity-time symmetry
condition for the dielectric
constant behaves simultaneously as a laser oscillator (i.e. it can emit
outgoing coherent waves) and as a CPA (i.e. it can fully absorb incoming
coherent waves with appropriate amplitudes and phases). Such a device can be
thus referred to as a -symmetric CPA-laser. The general
amplification/absorption features of the CPA-laser below lasing
threshold driven by two fields are determined.Comment: 5 pages; to be published in Phys. Rev. A (Rapid Communications
Half-spectral unidirectional invisibility in non-Hermitian periodic optical structures
The phenomenon of half-spectral unidirectional invisibility is introduced for
one-dimensional periodic optical structures with tailored real and imaginary
refractive index distributions in a non--symmetric configuration.
The effect refers to the property that the optical medium appears to be
invisible, both in reflection and transmission, below the Bragg frequency when
probed from one side, and above the Bragg frequency when probed from the
opposite side. Half-spectral invisibility is obtained by a combination of
in-phase index and gain gratings whose spatial amplitudes are related each
other by a Hilbert transform.Comment: 6 pages, 6 figure
Invisible defects in complex crystals
We show that invisible localized defects, i.e. defects that can not be
detected by an outside observer, can be realized in a crystal with an
engineered imaginary potential at the defect site. The invisible defects are
synthesized by means of supersymmetric (Darboux) transformations of an ordinary
crystal using band-edge wave functions to construct the superpotential. The
complex crystal has an entire real-valued energy spectrum and Bragg scattering
is not influenced by the defects. An example of complex crystal synthesis is
presented for the Mathieu potential
Zitterbewegung of optical pulses in nonlinear frequency conversion
Pulse walk-off in the process of sum frequency generation in a nonlinear
crystal is shown to be responsible for pulse jittering which is
reminiscent to the Zitterbewegung (trembling motion) of a relativistic freely
moving Dirac particle. An analytical expression for the pulse center of mass
trajectory is derived in the no-pump-depletion limit, and numerical examples of
Zitterbewegung are presented for sum frequency generation in periodically-poled
lithium niobate. The proposed quantum-optical analogy indicates that frequency
conversion in nonlinear optics could provide an experimentally accessible
simulator of the Dirac equation.Comment: to be published in Journal of Physics B: Atomic, Molecular & Optical
Physic
Dynamic localization in Glauber-Fock lattices
Glauber-Fock lattices refer to a special class of semi-infinite tight-binding
lattices with inhomogeneous hopping rates which are found in certain simple
solid-state, quantum optics and quantum field theoretical models. Here it is
shown that dynamic localization, i.e. suppression of quantum diffusion and
periodic quantum self-imaging by an external sinusoidal force [D.H. Dunlap and
V.M. Kenkre, Phys. Rev. B {\bf 34}, 3625 (1986)], can be exactly realized in
Glauber-Fock lattices, in spite of inhomogeneity of hopping rates and lattice
truncation.Comment: 3 figure
Coherent transfer by adiabatic passage in two-dimensional lattices
Coherent tunneling by adiabatic passage (CTAP) is a well-established
technique for robust spatial transport of quantum particles in linear chains.
Here we introduce two exactly-solvable models where the CTAP protocol can be
extended to two-dimensional lattice geometries. Such bi-dimensional lattice
models are synthesized from time-dependent second-quantization Hamiltonians, in
which the bosonic field operators evolve adiabatically like in an ordinary
three-level CTAP scheme thus ensuring adiabatic passage in Fock space.Comment: 17 pages, 6 figures, to appear in Annals of Physic
Reflectionless and invisible potentials in photonic lattices
An arbitrarily-shaped optical potential on a discrete photonic lattice, which
transversely drifts at a speed larger than the maximum one allowed by the light
cone of the lattice band, becomes reflectionless. Such an intriguing result,
which arises from the discrete translational symmetry of the lattice, is
peculiar to discretized light and does not have any counterpart for light
scattering in continuous optical media. A drifting non-Hermitian optical
potential of the Kramers-Kronig type is also an invisible potential, i.e. a
discrete optical beam crosses the drifting potential without being distorted,
delayed nor advanced.Comment: 6 pages, 3 figure
phase control in circular multicore fibers
We consider light dynamics in a circular multicore fiber with balanced gain
and loss core distribution, and show that transition from unbroken to broken
phases can be conveniently controlled by geometric twist of the
fiber. The twist introduces Peierls' phases in the coupling constants and thus
acts as an artificial gauge field. As an application, we discuss twist-induced
tuning of optical transmission in a six-core fiber with one lossy core.Comment: 6 pages, 4 figures; to appear in Optics Letter
Loschmidt echo and fidelity decay near an exceptional point
Non-Hermitian classical and open quantum systems near an exceptional point
(EP) are known to undergo strong deviations in their dynamical behavior under
small perturbations or slow cycling of parameters as compared to Hermitian
systems. Such a strong sensitivity is at the heart of many interesting
phenomena and applications, such as the asymmetric breakdown of the adiabatic
theorem, enhanced sensing, non-Hermitian dynamical quantum phase transitions
and photonic catastrophe. Like for Hermitian systems, the sensitivity to
perturbations on the dynamical evolution can be captured by Loschmidt echo and
fidelity after imperfect time reversal or quench dynamics. Here we disclose a
rather counterintuitive phenomenon in certain non-Hermitian systems near an EP,
namely the deceleration (rather than acceleration) of the fidelity decay and
improved Loschmidt echo as compared to their Hermitian counterparts, despite
large (non-perturbative) deformation of the energy spectrum introduced by the
perturbations. This behavior is illustrated by considering the fidelity decay
and Loschmidt echo for the single-particle hopping dynamics on a tight-binding
lattice under an imaginary gauge field.Comment: 11 pages, 6 figures, to appear in Annalen der Physi
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