41 research outputs found
Antiferromagnetic cavity optomagnonics
Currently there is a growing interest in studying the coherent interaction between magnetic systems and electromagnetic radiation in a cavity, prompted partly by possible applications in hybrid quantum systems. We propose a multimode cavity optomagnonic system based on antiferromagnetic insulators, where optical photons couple coherently to the two homogeneous magnon modes of the antiferromagnet. These have frequencies typically in the THz range, a regime so far mostly unexplored in the realm of coherent interactions, and which makes antiferromagnets attractive for quantum transduction from THz to optical frequencies. We derive the theoretical model for the coupled system, and show that it presents unique characteristics. In particular, if the antiferromagnet presents hard-axis magnetic anisotropy, the optomagnonic coupling can be tuned by a magnetic field applied along the easy axis. This allows us to bring a selected magnon mode into and out of a dark mode, providing an alternative for a quantum memory protocol. The dynamical features of the driven system present unusual behavior due to optically induced magnon-magnon interactions, including regions of magnon heating for a red-detuned driving laser. The multimode character of the system is evident in a substructure of the optomagnonically induced transparency window
Magnon heralding in cavity optomagnonics
In the emerging field of cavity optomagnonics, photons are coupled coherently
to magnons in solid-state systems. These new systems are promising for
implementing hybrid quantum technologies. Being able to prepare Fock states in
such platforms is an essential step towards the implementation of quantum
information schemes. We propose a magnon-heralding protocol to generate a
magnon Fock state by detecting an optical cavity photon. Due to the
peculiarities of the optomagnonic coupling, the protocol involves two distinct
cavity photon modes. Solving the quantum Langevin equations of the coupled
system, we show that the temporal scale of the heralding is governed by the
magnon-photon cooperativity and derive the requirements for generating high
fidelity magnon Fock states. We show that the nonclassical character of the
heralded state, which is imprinted in the autocorrelation of an optical "read"
mode, is only limited by the magnon lifetime for small enough temperatures. We
address the detrimental effects of nonvacuum initial states, showing that high
fidelity Fock states can be achieved by actively cooling the system prior to
the protocol.Comment: 17 pages, 14 figures. Correction of typos, version as publishe
Magnon-Phonon Quantum Correlation Thermometry
A large fraction of quantum science and technology requires low-temperature environments such as those afforded by dilution refrigerators. In these cryogenic environments, accurate thermometry can be difficult to implement, expensive, and often requires calibration to an external reference. Here, we theoretically propose a primary thermometer based on measurement of a hybrid system consisting of phonons coupled via a magnetostrictive interaction to magnons. Thermometry is based on a cross-correlation measurement in which the spectrum of back-action driven motion is used to scale the thermomechanical motion, providing a direct measurement of the phonon temperature independent of experimental parameters. Combined with a simple low-temperature compatible microwave cavity readout, this primary thermometer is expected to become a promising alternative for thermometry below 1 K
Dynamical Backaction Evading Magnomechanics
The interaction between magnons and mechanical vibrations dynamically modify
the properties of the mechanical oscillator, such as its frequency and decay
rate. Known as dynamical backaction, this effect is the basis for many
theoretical protocols, such as entanglement generation or mechanical
ground-state cooling. However, dynamical backaction is also detrimental for
specific applications. Here, we demonstrate the implementation of a cavity
magnomechanical measurement that fully evades dynamical backaction effects.
Through careful engineering, the magnomechanical scattering rate into the
hybrid magnon-photon modes can be precisely matched, eliminating dynamical
backaction damping. Backaction evasion is confirmed via the measurement of a
drive-power-independent mechanical linewidth.Comment: 6 pages, 5 figure
Magnomechanical backaction corrections due to coupling to higher order Walker modes and Kerr nonlinearities
The radiation pressure-like coupling between magnons and phonons in magnets
can modify the phonon frequency (magnomechanical spring effect) and decay rate
(magnomechanical decay) via dynamical backaction. Such effects have been
recently observed by coupling the uniform magnon mode of a magnetic sphere (the
Kittel mode) to a microwave cavity. In particular, the ability to evade
backaction effects was demonstrated [C.A. Potts et al., arXiv:2211.13766
[quant-ph] (2022)], a requisite for applications such as magnomechanical based
thermometry. However, deviations were observed from the predicted
magnomechanical decay rate within the standard theoretical model. In this work,
we account for these deviations by considering corrections due to (i) magnetic
Kerr nonlinearities and (ii) the coupling of phonons to additional magnon
modes. Provided that such additional modes couple weakly to the driven cavity,
our model yields a correction proportional to the average Kittel magnon mode
occupation. We focus our results on magnetic spheres, where we show that the
magnetostatic Walker modes couple to the relevant mechanical modes as
efficiently as the Kittel mode. Our model yields excellent agreement with the
experimental data.Comment: 20 pages, 9 figure
Dynamical Backaction Magnomechanics
Dynamical backaction resulting from radiation pressure forces in
optomechanical systems has proven to be a versatile tool for manipulating
mechanical vibrations. Notably, dynamical backaction has resulted in the
cooling of a mechanical resonator to its ground-state, driving phonon lasing,
the generation of entangled states, and observation of the optical-spring
effect. In certain magnetic materials, mechanical vibrations can interact with
magnetic excitations (magnons) via the magnetostrictive interaction, resulting
in an analogous magnon-induced dynamical backaction. In this article, we
directly observe the impact of magnon-induced dynamical backaction on a
spherical magnetic sample's mechanical vibrations. Moreover, dynamical
backaction effects play a crucial role in many recent theoretical proposals;
thus, our work provides the foundation for future experimental work pursuing
many of these theoretical proposals.Comment: Accepted version with appendice
Tuning the pseudospin polarization of graphene by a pseudo-magnetic field
One of the intriguing characteristics of honeycomb lattices is the appearance
of a pseudo-magnetic field as a result of mechanical deformation. In the case
of graphene, the Landau quantization resulting from this pseudo-magnetic field
has been measured using scanning tunneling microscopy. Here we show that a
signature of the pseudo-magnetic field is a local sublattice symmetry breaking
observable as a redistribution of the local density of states. This can be
interpreted as a polarization of graphene's pseudospin due to a strain induced
pseudo-magnetic field, in analogy to the alignment of a real spin in a magnetic
field. We reveal this sublattice symmetry breaking by tunably straining
graphene using the tip of a scanning tunneling microscope. The tip locally
lifts the graphene membrane from a SiO support, as visible by an increased
slope of the curves. The amount of lifting is consistent with molecular
dynamics calculations, which reveal a deformed graphene area under the tip in
the shape of a Gaussian. The pseudo-magnetic field induced by the deformation
becomes visible as a sublattice symmetry breaking which scales with the lifting
height of the strained deformation and therefore with the pseudo-magnetic field
strength. Its magnitude is quantitatively reproduced by analytic and
tight-binding models, revealing fields of 1000 T. These results might be the
starting point for an effective THz valley filter, as a basic element of
valleytronics.Comment: Revised manuscript: streamlined the abstract and introduction, added
methods to supplement, Nano Letters, 201
The electronic properties of bilayer graphene
We review the electronic properties of bilayer graphene, beginning with a
description of the tight-binding model of bilayer graphene and the derivation
of the effective Hamiltonian describing massive chiral quasiparticles in two
parabolic bands at low energy. We take into account five tight-binding
parameters of the Slonczewski-Weiss-McClure model of bulk graphite plus intra-
and interlayer asymmetry between atomic sites which induce band gaps in the
low-energy spectrum. The Hartree model of screening and band-gap opening due to
interlayer asymmetry in the presence of external gates is presented. The
tight-binding model is used to describe optical and transport properties
including the integer quantum Hall effect, and we also discuss orbital
magnetism, phonons and the influence of strain on electronic properties. We
conclude with an overview of electronic interaction effects.Comment: review, 31 pages, 15 figure
Quasiparticles of strongly correlated Fermi liquids at high temperatures and in high magnetic fields
Strongly correlated Fermi systems are among the most intriguing, best
experimentally studied and fundamental systems in physics. There is, however,
lack of theoretical understanding in this field of physics. The ideas based on
the concepts like Kondo lattice and involving quantum and thermal fluctuations
at a quantum critical point have been used to explain the unusual physics.
Alas, being suggested to describe one property, these approaches fail to
explain the others. This means a real crisis in theory suggesting that there is
a hidden fundamental law of nature. It turns out that the hidden fundamental
law is well forgotten old one directly related to the Landau---Migdal
quasiparticles, while the basic properties and the scaling behavior of the
strongly correlated systems can be described within the framework of the
fermion condensation quantum phase transition (FCQPT). The phase transition
comprises the extended quasiparticle paradigm that allows us to explain the
non-Fermi liquid (NFL) behavior observed in these systems. In contrast to the
Landau paradigm stating that the quasiparticle effective mass is a constant,
the effective mass of new quasiparticles strongly depends on temperature,
magnetic field, pressure, and other parameters. Our observations are in good
agreement with experimental facts and show that FCQPT is responsible for the
observed NFL behavior and quasiparticles survive both high temperatures and
high magnetic fields.Comment: 17 pages, 17 figures. Dedicated to 100th anniversary of A.B.Migdal
birthda