52 research outputs found
Intense squeezed light from lasers with sharply nonlinear gain at optical frequencies
Non-classical states of light, such as number-squeezed light, with
fluctuations below the classical shot noise level, have important uses in
metrology, communication, quantum information processing, and quantum
simulation. However, generating these non-classical states of light, especially
with high intensity and high degree of squeezing, is challenging. To address
this problem, we introduce a new concept which uses gain to generate intense
sub-Poissonian light at optical frequencies. It exploits a strongly nonlinear
gain for photons which arises from a combination of frequency-dependent gain
and Kerr nonlinearity. In this laser architecture, the interaction between the
gain medium and Kerr nonlinearity suppresses the spontaneous emission at high
photon number states, leading to a strong "negative feedback" that suppresses
photon-number fluctuations. We discuss realistic implementations of this
concept based on the use of solid-state gain media in laser cavities with Kerr
nonlinear materials, showing how 90% squeezing of photon number fluctuations
below the shot noise level can be realized
Fock lasers based on deep-strong coupling of light and matter
Light and matter can now interact in a regime where their coupling is
stronger than their bare energies. This deep-strong coupling (DSC) regime of
quantum electrodynamics promises to challenge many conventional assumptions
about the physics of light and matter. Here, we show how light and matter
interactions in this regime give rise to electromagnetic nonlinearities
dramatically different from those of naturally existing materials. Excitations
in the DSC regime act as photons with a linear energy spectrum up to a critical
excitation number, after which, the system suddenly becomes strongly
anharmonic, thus acting as an effective intensity-dependent nonlinearity of an
extremely high order. We show that this behavior allows for N-photon blockade
(with ), enabling qualitatively new kinds of quantum light sources.
For example, this nonlinearity forms the basis for a new type of gain medium,
which when integrated into a laser or maser, produces large Fock states (rather
than coherent states). Such Fock states could in principle have photon numbers
orders of magnitude larger than any realized previously, and would be protected
from dissipation by a new type of equilibrium between nonlinear gain and linear
loss. We discuss paths to experimental realization of the effects described
here
Two photon emission from superluminal and accelerating index perturbations
Sources of photons with controllable quantum properties such as entanglement
and squeezing are desired for applications in quantum information, metrology,
and sensing. However, fine-grained control over these properties is hard to
achieve, especially for two-photon sources. Here, we propose a new mechanism
for generating entangled and squeezed photon pairs using superluminal and/or
accelerating modulations of the refractive index in a medium. By leveraging
time-changing dielectric media, where quantum vacuum fluctuations of the
electromagnetic field can be converted into photon pairs, we show that energy-
and momentum-conservation in multi-mode systems give rise to frequency and
angle correlations of photon pairs which are controlled by the trajectory of
the index modulation. These radiation effects are two-photon analogues of
Cherenkov and synchrotron radiation by moving charged particles such as free
electrons. We find the particularly intriguing result that synchrotron-like
radiation into photon pairs exhibits frequency correlations which can enable
the realization of a heralded single photon frequency comb. We conclude with a
general discussion of experimental viability, showing how solitons, ultrashort
pulses, and nonlinear waveguides may enable pathways to realize this two-photon
emission mechanism. For completeness, we discuss in the Supplementary
Information how these effects, sensitive to the local density of photonic
states, can be strongly enhanced using photonic nanostructures. As an example,
we show that index modulations propagating near the surface of graphene produce
entangled pairs of graphene plasmons with high efficiency, leading to
additional experimental opportunities
Creating large Fock states and massively squeezed states in optics using systems with nonlinear bound states in the continuum
The quantization of the electromagnetic field leads directly to the existence
of quantum mechanical states, called Fock states, with an exact integer number
of photons. Despite these fundamental states being long-understood, and despite
their many potential applications, generating them is largely an open problem.
For example, at optical frequencies, it is challenging to deterministically
generate Fock states of order two and beyond. Here, we predict the existence of
a new effect in nonlinear optics, which enables the deterministic generation of
large Fock states at arbitrary frequencies. The effect, which we call an
n-photon bound state in the continuum, is one in which a photonic resonance
(such as a cavity mode) becomes lossless when a precise number of photons n is
inside the resonance. Based on analytical theory and numerical simulations, we
show that these bound states enable a remarkable phenomenon in which a coherent
state of light, when injected into a system supporting this bound state, can
spontaneously evolve into a Fock state of a controllable photon number. This
effect is also directly applicable for creating (highly) squeezed states of
light, whose photon number fluctuations are (far) below the value expected from
classical physics (i.e., shot noise). We suggest several examples of systems to
experimentally realize the effects predicted here in nonlinear nanophotonic
systems, showing examples of generating both optical Fock states with large n
(n > 10), as well as more macroscopic photonic states with very large
squeezing, with over 90% less noise (10 dB) than the classical value associated
with shot noise
Entangling extreme ultraviolet photons through strong field pair generation
Entangled photon pairs are a vital resource for quantum information,
computation, and metrology. Although these states are routinely generated at
optical frequencies, sources of quantum of light are notably lacking at extreme
ultraviolet (XUV) and soft X-ray frequencies. Here, we show that strongly
driven systems used for high harmonic generation (HHG) can become versatile
sources of entangled photon pairs at these high frequencies. We present a
general theory of photon pair emission from non-perturbatively driven systems,
which we refer to as "strong field pair generation" (SFPG). We show that
strongly driven noble gases can generate thousands of entangled pairs per shot
over a large XUV bandwidth. The emitted pairs have distinctive properties in
angle and frequency, which can be exploited to discriminate them from the
background HHG signal. We connect SFPG theory to the three-step-model of HHG,
showing that this pair emission originates from the impact of high frequency
vacuum fluctuations on electron recombination. The light produced by SFPG
exhibits attosecond Hong-Ou-Mandel correlations, and can be leveraged as a
source of heralded single photon attosecond pulses. Our findings aid ongoing
efforts to propel quantum optics into the XUV and beyond
Study protocol for iQuit in Practice: a randomised controlled trial to assess the feasibility, acceptability and effectiveness of tailored web- and text-based facilitation of smoking cessation in primary care.
BACKGROUND: Primary care is an important setting for smoking cessation interventions. There is evidence for the effectiveness of tailored interventions for smoking cessation, and text messaging interventions for smoking cessation show promise. The intervention to be evaluated in this trial consists of two components: (1) a web-based program designed to be used by a practice nurse or other smoking cessation advisor (SCA); the program generates a cessation advice report that is highly tailored to relevant characteristics of the smoker; and (2) a three-month programme of automated tailored text messages sent to the smoker's mobile phone. The objectives of the trial are to assess the acceptability and feasibility of the intervention and to estimate the short-term effectiveness of the intervention in increasing the quit rate compared with usual care alone. METHODS/DESIGN: The design is a two parallel group randomised controlled trial (RCT). 600 smokers who want to quit will be recruited in up to 30 general practices in the East of England. During a consultation with an SCA, they will be individually randomised by computer program to usual care (Control) or to usual care plus the iQuit system (Intervention). At the four-week follow-up appointment, the SCA will record smoking status and measure carbon monoxide level. There will be two further follow-ups, at eight weeks and six months from randomisation date, by postal questionnaire sent from and returned to the study centre or by telephone interview conducted by a research interviewer. The primary outcome will be self-reported abstinence for at least two weeks at eight weeks. A sample size of 300 per group would give 80% power to detect an increase in quit rate from 20% to 30% (alpha = 0.05, 2-sided test). The main analyses of quit rates will be conducted on an intention-to-treat basis, making the usual assumption that participants lost to follow up are smoking. DISCUSSION: This trial will focus on acceptability, feasibility and short-term effectiveness. The findings will be used to refine the intervention and to inform the decision to proceed to a pragmatic trial to estimate longer-term effectiveness and cost-effectiveness. TRIAL REGISTRATION: ISRCTN56702353.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are
Randomized controlled trial to assess the short-term effectiveness of tailored web- and text-based facilitation of smoking cessation in primary care (iQuit in practice).
AIMS: To estimate the short-term effectiveness, feasibility and acceptability of a smoking cessation intervention (the iQuit system) that consists of tailored printed and Short Message Service (SMS) text message self-help delivered as an adjunct to cessation support in primary care to inform the design of a definitive trial. DESIGN: A stratified two parallel-group randomized controlled trial comparing usual care (control) with usual care plus the iQuit system (intervention), delivered by primary care nurses/healthcare assistants who were blinded to the allocation sequence. SETTING: Thirty-two general practice (GP) surgeries in England, UK. PARTICIPANTS: A total of 602 smokers initiating smoking cessation support from their local GP surgery were randomized (control n = 303, intervention n = 299). MEASUREMENTS: Primary outcome was self-reported 2-week point prevalence abstinence at 8 weeks follow-up. Secondary smoking outcomes and feasibility and acceptability measures were collected at 4 weeks after quit date, 8 weeks and 6 months follow-up. FINDINGS: There were no significant between-group differences in the primary outcome [control 40.3%, iQuit 45.2%; odds ratio (OR) = 1.22, 95% confidence interval (CI) = 0.88-1.69] or in secondary short-term smoking outcomes. Six-month prolonged abstinence was significantly higher in the iQuit arm (control 8.9%, iQuit 15.1%; OR = 1.81, 95% CI = 1.09-3.01). iQuit support took on average 7.7 minutes (standard deviation = 4.0) to deliver and 18.9% (95% CI = 14.8-23.7%) of intervention participants discontinued the text message support during the programme. CONCLUSIONS: Tailored printed and text message self-help delivered alongside routine smoking cessation support in primary care does not significantly increase short-term abstinence, but may increase long-term abstinence and demonstrated feasibility and acceptability compared with routine cessation support alone
Biasing the quantum vacuum to control macroscopic probability distributions
One of the most important insights of quantum field theory is that
electromagnetic fields must fluctuate. Even in the vacuum state, the electric
and magnetic fields have a nonzero variance, leading to ubiquitous effects such
as spontaneous emission, the Lamb shift, the Casimir effect, and more. These
"vacuum fluctuations" have also been harnessed as a source of perfect
randomness, for example to generate perfectly random photonic bits. Despite
these achievements, many potential applications of quantum randomness in fields
such as probabilistic computing rely on controllable probability distributions,
which have not yet been realized on photonic platforms. In this work, we show
that the injection of vacuum-level "bias" fields into a multi-stable optical
system enables a controllable source of "biased" quantum randomness. We
demonstrate this concept in an optical parametric oscillator (OPO). Ordinarily,
an OPO initiated from the ground state develops a signal field in one of two
degenerate phase states (0 and ) with equal probability. By injecting bias
pulses which contain less than one photon on average, we control the
probabilities associated with the two output states, leading to the first
controllable photonic probabilistic bit (p-bit). We shed light on the physics
behind this process, showing quantitative agreement between theory and
experiment. Finally, we demonstrate the potential of our approach for sensing
sub-photon level fields by showing that our system is sensitive to the temporal
shape of bias field pulses far below the single photon level. Our results
suggest a new platform for the study of stochastic quantum dynamics in
nonlinear driven-dissipative systems, and point toward possible applications in
ultrafast photonic probabilistic computing, as well as the sensing of extremely
weak fields
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