220 research outputs found
Mean parity of single quantum excitation of some optical fields in thermal environments
The mean parity (the Wigner function at the origin) of excited binomial
states, excited coherent states and excited thermal states in thermal channel
is investigated in details. It is found that the single-photon excited binomial
state and the single-photon excited coherent state exhibit certain similarity
in the aspect of their mean parity in the thermal channel. We show the negative
mean parity can be regarded as an indicator of nonclassicality of single-photon
excitation of optical fields with a little coherence, especially for the
single-photon excited thermal states.Comment: 4 pages, 4 figures, RevTex4; PACS numbers: 42.50.Dv, 03.65.Yz,
05.40.Ca; Three typo errors have been correcte
Non-Hermitian trimers: PT-symmetry versus pseudo-Hermiticity
We study a structure composed of three coupled waveguides with gain and loss, a non-Hermitian
trimer. We demonstrate that the mode spectrum can be entirely real if the waveguides are placed in a
special order and at certain distances between each other. Such structures generally lack a spatial
symmetry, in contrast to parity-time symmetric trimers which are known to feature a real spectrum.
We also determine a threshold for wave amplification and analyse the scattering properties of such
non-conservative systems embedded into a chain of conservative waveguides.SVS and AAS were supported by the Australian Research Council (ARC), Discovery Project DP160100619. SVS
acknowledges financial support from the Russian Foundation for Basic Research, grant No.15-31-20037 mol_a
Creating and Verifying a Quantum Superposition in a Micro-optomechanical System
Micro-optomechanical systems are central to a number of recent proposals for
realizing quantum mechanical effects in relatively massive systems. Here we
focus on a particular class of experiments which aim to demonstrate massive
quantum superpositions, although the obtained results should be generalizable
to similar experiments. We analyze in detail the effects of finite temperature
on the interpretation of the experiment, and obtain a lower bound on the degree
of non-classicality of the cantilever. Although it is possible to measure the
quantum decoherence time when starting from finite temperature, an unambiguous
demonstration of a quantum superposition requires the mechanical resonator to
be in or near the ground state. This can be achieved by optical cooling of the
fundamental mode, which also provides a method to measure the mean phonon
number in that mode. We also calculate the rate of environmentally induced
decoherence and estimate the timescale for gravitational collapse mechanisms as
proposed by Penrose and Diosi. In view of recent experimental advances,
practical considerations for the realization of the described experiment are
discussed.Comment: 19 pages, 8 figures, published in New J. Phys. 10 095020 (2008);
minor revisions to improve clarity; fixed possibly corrupted figure
Nonclassical properties of states engineered by superpositions of quantum operations on classical states
We consider an experimentally realizable scheme for manipulating quantum
states using a general superposition of products of field annihilation
() and creation () operators of the type (), with . Such an
operation, when applied on states with classical features, is shown to
introduce strong nonclassicality. We quantify the generated degree of
nonclassicality by the negative volume of Wigner distribution in the phase
space and investigate two other observable nonclassical features,
sub-Poissonian statistics and squeezing. We find that the operation introduces
negativity in the Wigner distribution of an input coherent state and changes
the Gaussianity of an input thermal state. This provides the possibility of
engineering quantum states with specific nonclassical features.Comment: 19 pages, IOPclass(iopart.cls
Free and immobilized matrix molecules: impairing ionization by quenching secondary ion formation in laser desorption MS
Within the last 25 years, matrix-assisted laser desorption ionization (MALDI) has become a powerful analytical tool in mass spectrometry (MS). While the method has been successfully applied to characterize large organic molecules such as proteins, sugars and polymers, its utilization for small molecules (≤ 600 Da) is significantly impaired by the coformation of matrix ions. Reducing or eliminating matrix-related signals has been subject of many studies. Some of which propose the enhancement of so-called matrix suppression effects, while others suggest the replacement of matrix molecules by materials such as microporous silicon. Alternatively, the immobilization of matrix molecules by utilizing them as self-assembled monolayers (SAMs) has been discussed. In continuation of this research, the current manuscript focuses on the elucidation of ion formation processes occurring on the surface of light absorbing SAMs. Ion yields obtained by free and immobilized matrix molecules as well as those generated by matrix-free gold film-assisted laser desorption ionization (GF-LDI) were compared. Experiments showed that the formation of strong analyte signals essentially required the presence of free matrix molecules, while the immobilization of the latter severely impaired ionization. The observed effect inversely correlated with the surface coverage of SAMs determined by cyclic voltammetry (CV). Based on these findings, the MS signal generated on light absorbing SAMs could be used supplementary to CV for determining the surface coverage of light absorbing SAMs
Cardiac output by model flow method from intra-arterial and finger tip pulse pressure profiles
Modelflow®, when applied to non-invasive fingertip pulse pressure recordings, is a poor predictor of cardiac output (Q’ litre· min-1). The use of constants established from the aortic elastic characteristics, which differ from those of finger arteries, may introduce signal distortions, leading to errors in computing Q’. We therefore hypothesized that peripheral recording of pulse pressure profiles undermines the measurement of Q’ withModelflow®, so we compared Modelflow® beat-by-beat Q’ values obtained simultaneously non-invasively from the finger and invasively from the radial artery at rest and during exercise. Seven subjects (age, 24.0 + - 2.9 years; weight, 81.2 + - 12.6 kg) rested, then exercised at 50 and 100 W, carrying a catheter with a pressure head in the left radial artery and the photoplethysmographic cuff of a finger pressure device on the third and fourth fingers of the contralateral hand. Pulse pressure from both devices was recorded simultaneously and stored on a PC for subsequent Q’ computation. The mean values of systolic, diastolic and mean arterial pressure at rest and exercise steady state were significantly (P < 0.05) lower from the finger than the intra-arterial catheter. The corresponding mean steady-state Q’ obtained from the finger (Q’porta) was significantly (P < 0.05) higher than that computed from the intra-arterial recordings (Q’pia). The line relating beat-by-beat Q’porta and Q’pia was y = 1.55x - 3.02 (r2 = 0.640). The bias was 1.44 litre · min-1 and the precision was 2.84 litre · min-1.The slope of this line was significantly higher than 1, implying a systematic overestimate of Q’ by Q’porta with respect to Q’pia. Consistent with the tested hypothesis, these results demonstrate that pulse pressure profiles from the finger provide inaccurate absolute Q’ values with respect to the radial artery, and therefore cannot be used without correction with a calibration factor calculated previously by measuring Q’ with an independent method
Phase I dynamics of cardiac output, systemic O2 delivery and lung O2 uptake at exercise onset in men in acute normobaric hypoxia.
We tested the hypothesis that vagal withdrawal plays a role in the rapid (phase I) cardiopulmonary response to exercise. To this aim, in five men (24.6+/-3.4 yr, 82.1+/-13.7 kg, maximal aerobic power 330+/-67 W), we determined beat-by-beat cardiac output (Q), oxygen delivery (QaO2), and breath-by-breath lung oxygen uptake (VO2) at light exercise (50 and 100 W) in normoxia and acute hypoxia (fraction of inspired O2=0.11), because the latter reduces resting vagal activity. We computed Q from stroke volume (Qst, by model flow) and heart rate (fH, electrocardiography), and QaO2 from Q and arterial O2 concentration. Double exponentials were fitted to the data. In hypoxia compared with normoxia, steady-state fH and Q were higher, and Qst and VO2 were unchanged. QaO2 was unchanged at rest and lower at exercise. During transients, amplitude of phase I (A1) for VO2 was unchanged. For fH, Q and QaO2, A1 was lower. Phase I time constant (tau1) for QaO2 and VO2 was unchanged. The same was the case for Q at 100 W and for fH at 50 W. Qst kinetics were unaffected. In conclusion, the results do not fully support the hypothesis that vagal withdrawal determines phase I, because it was not completely suppressed. Although we can attribute the decrease in A1 of fH to a diminished degree of vagal withdrawal in hypoxia, this is not so for Qst. Thus the dual origin of the phase I of Q and QaO2, neural (vagal) and mechanical (venous return increase by muscle pump action), would rather be confirmed
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