98 research outputs found
Spin conservation in high-order-harmonic generation using bicircular fields
We present an alternative theoretical model for a recent experiment
[A.Fleischer et al., Nature Photon. 8, 543 (2014)] which used bichromatic,
counter-rotating high intensity laser pulses to probe the conservation of spin
angular momentum in high harmonic generation. We separate elliptical
polarizations into independent circular fields with definite angular momentum,
instead of using the expectation value of spin for each photon in the
conservation equation, and we find good agreement with the experimental
results. In our description the generation of each individual harmonic
conserves spin angular momentum, in contrast to the model proposed by Fleischer
et al. Our model also correctly describes analogous processes in standard
perturbative optics.Comment: Final changes from published version. Updated license to CC-BY-NC-S
High-harmonic generation: taking control of polarization
The ability to control the polarization of short-wavelength radiation generated by high-harmonic generation is useful not only for applications but also for testing conservation laws in physics
On the Spectrum of Field Quadratures for a Finite Number of Photons
The spectrum and eigenstates of any field quadrature operator restricted to a
finite number of photons are studied, in terms of the Hermite polynomials.
By (naturally) defining \textit{approximate} eigenstates, which represent
highly localized wavefunctions with up to photons, one can arrive at an
appropriate notion of limit for the spectrum of the quadrature as goes to
infinity, in the sense that the limit coincides with the spectrum of the
infinite-dimensional quadrature operator. In particular, this notion allows the
spectra of truncated phase operators to tend to the complete unit circle, as
one would expect. A regular structure for the zeros of the Christoffel-Darboux
kernel is also shown.Comment: 16 pages, 11 figure
Principal frequency of an ultrashort laser pulse
We introduce an alternative definition of the main frequency of an ultrashort
laser pulse, the principal frequency . This parameter is
complementary to the most accepted and widely used carrier frequency
. Given the fact that these ultrashort pulses, also known as
transients, have a temporal width comprising only few cycles of the carrier
wave, corresponding to a spectral bandwidth covering several
octaves, describes, in a more precise way, the dynamics driven by
these sources. We present examples where, for instance, is able to
correctly predict the high-order harmonic cutoff independently of the carrier
envelope phase. This is confirmed by solving the time-dependent Schr\"odinger
equation in reduced dimensions, supplemented with the time-analysis of the
quantum spectra, where it is possible to observe how the sub-cycle electron
dynamics is better described using . The concept of ,
however, can be applied to a large variety of scenarios, not only within the
strong field physics domain.Comment: 11 pages, 6 figures, accepted in PR
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Conservation laws for electron vortices in strong-field ionisation
We investigate twisted electrons with a well-defined orbital angular momentum, which have been ionised via a strong laser field. By formulating a new variant of the well-known strong field approximation, we are able to derive conservation laws for the angular momenta of twisted electrons in the cases of linear and circularly polarised fields. In the case of linear fields, we demonstrate that the orbital angular momentum of the twisted electron is determined by the magnetic quantum number of the initial bound state. The condition for the circular field can be related to the famous ATI peaks, and provides a new interpretation for this fundamental feature of photoelectron spectra. We find the length of the circular pulse to be a vital factor in this selection rule and, employing an effective frequency, we show that the photoelectron OAM emission spectra are sensitive to the parity of the number of laser cycles. This work provides the basic theoretical framework with which to understand the OAM of a photoelectron undergoing strong field ionisation
Quantum optical analysis of high-order harmonic generation in H molecular ions
We present a comprehensive theoretical investigation of high-order harmonic
generation in H molecular ions within a quantum optical framework. Our
study focuses on characterizing various quantum optical and quantum information
measures, highlighting the versatility of HHG in two-center molecules towards
quantum technology applications. We demonstrate the emergence of entanglement
between electron and light states after the laser-matter interaction. We also
identify the possibility of obtaining non-classical states of light in targeted
frequency modes by conditioning on specific electronic quantum states, which
turn out to be crucial in the generation of highly non-classical entangled
states between distinct sets of harmonic modes. Our findings open up avenues
for studying strong-laser field-driven interactions in molecular systems, and
suggest their applicability to quantum technology applications.Comment: 21 pages (14 main text + 7 appendix), 9 figures (8 main text + 1
appendix
Entanglement and non-classical states of light in a strong-laser driven solid-state system
The development of sources delivering non-classical states of light is one of
the main needs for applications of optical quantum information science. Here,
we demonstrate the generation of non-classical states of light using
strong-laser fields driving a solid-state system, by using the process of
high-order harmonic generation, where an electron tunnels out of the parent
site and, later on, recombines on it emitting high-order harmonic radiation, at
the expense of affecting the driving laser field. Since in solid-state systems
the recombination of the electron can be delocalized along the material, the
final state of the electron determines how the electromagnetic field gets
affected because of the laser-matter interaction, leading to the generation of
entanglement between the electron and the field. These features can be enhanced
by applying conditioning operations, i.e., quantum operations based on the
measurement of high-harmonic radiation. We study non-classical features present
in the final quantum optical state, and characterize the amount of entanglement
between the light and the electrons in the solid. The work sets the foundation
for the development of compact solid-state-based non-classical light sources
using strong-field physics.Comment: We present a different formulation to that of the previous version,
more in line with the approach followed in our previous works. 12 pages (8
main text + 4 Methods), 4 figures. Comments are welcom
Strong laser physics, non-classical light states and quantum information science
Strong laser physics is a research direction that relies on the use of
high-power lasers and has led to fascinating achievements ranging from
relativistic particle acceleration to attosecond science. On the other hand,
quantum optics has been built on the use of low photon number sources and has
opened the way for groundbreaking discoveries in quantum technology, advancing
investigations ranging from fundamental tests of quantum theory to quantum
information processing. Despite the tremendous progress, until recently these
directions have remained disconnected. This is because, the majority of the
interactions in the strong-field limit have been successfully described by
semi-classical approximations treating the electromagnetic field classically,
as there was no need to include the quantum properties of the field to explain
the observations. The link between strong laser physics, quantum optics, and
quantum information science has been developed in the recent past. Studies
based on fully quantized and conditioning approaches have shown that intense
laser--matter interactions can be used for the generation of controllable
entangled and non-classical light states. This achievement opens the way for a
vast number of investigations stemming from the symbiosis of strong laser
physics, quantum optics, and quantum information science. Here, after an
introduction to the fundamentals of these research directions, we report on the
recent progress in the fully quantized description of intense laser--matter
interaction and the methods that have been developed for the generation of
non-classical light states and entangled states. Also, we discuss the future
directions of non-classical light engineering using strong laser fields, and
the potential applications in ultrafast and quantum information science.Comment: 60 pages, 20 figures. Comments are welcom
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