924 research outputs found
Continuous-variable sampling from photon-added or photon-subtracted squeezed states
We introduce a new family of quantum circuits in Continuous Variables and we
show that, relying on the widely accepted conjecture that the polynomial
hierarchy of complexity classes does not collapse, their output probability
distribution cannot be efficiently simulated by a classical computer. These
circuits are composed of input photon-subtracted (or photon-added) squeezed
states, passive linear optics evolution, and eight-port homodyne detection. We
address the proof of hardness for the exact probability distribution of these
quantum circuits by exploiting mappings onto different architectures of
sub-universal quantum computers. We obtain both a worst-case and an
average-case hardness result. Hardness of Boson Sampling with eight-port
homodyne detection is obtained as the zero squeezing limit of our model. We
conclude with a discussion on the relevance and interest of the present model
in connection to experimental applications and classical simulations.Comment: 11 pages, 6 figure
Weighted complex projective 2-designs from bases: optimal state determination by orthogonal measurements
We introduce the problem of constructing weighted complex projective
2-designs from the union of a family of orthonormal bases. If the weight
remains constant across elements of the same basis, then such designs can be
interpreted as generalizations of complete sets of mutually unbiased bases,
being equivalent whenever the design is composed of d+1 bases in dimension d.
We show that, for the purpose of quantum state determination, these designs
specify an optimal collection of orthogonal measurements. Using highly
nonlinear functions on abelian groups, we construct explicit examples from d+2
orthonormal bases whenever d+1 is a prime power, covering dimensions d=6, 10,
and 12, for example, where no complete sets of mutually unbiased bases have
thus far been found.Comment: 28 pages, to appear in J. Math. Phy
On the universality of small scale turbulence
The proposed universality of small scale turbulence is investigated for a set
of measurements in a cryogenic free jet with a variation of the Reynolds number
(Re) from 8500 to 10^6. The traditional analysis of the statistics of velocity
increments by means of structure functions or probability density functions is
replaced by a new method which is based on the theory of stochastic Markovian
processes. It gives access to a more complete characterization by means of
joint probabilities of finding velocity increments at several scales. Based on
this more precise method our results call in question the concept of
universality.Comment: 4 pages, 4 figure
From the Bloch sphere to phase space representations with the Gottesman-Kitaev-Preskill encoding
In this work, we study the Wigner phase-space representation of qubit states
encoded in continuous variables (CV) by using the Gottesman-Kitaev-Preskill
(GKP) mapping. We explore a possible connection between resources for universal
quantum computation in discrete-variable (DV) systems, i.e. non-stabilizer
states, and negativity of the Wigner function in CV architectures, which is a
necessary requirement for quantum advantage. In particular, we show that the
lowest Wigner logarithmic negativity of qubit states encoded in CV with the GKP
mapping corresponds to encoded stabilizer states, while the maximum negativity
is associated with the most non-stabilizer states, H-type and T-type quantum
states.Comment: (v1) Accepted for publication in the Springer's "Mathematics for
Industry" series. (v2) Typo in the abstract fixed; URL of the conference
where the paper has been presented added: International Symposium on
Mathematics, Quantum Theory, and Cryptography (MQC), held in September 2019
in Fukuoka, Japan (https://www.mqc2019.org/mqc2019/program
Evidence for Exotic J^{PC}=1^{-+} Meson Production in the Reaction pi- p --> eta pi- p at 18 GeV/c
Details of the analysis of the eta pi- system studied in the reaction pi^{-}
p --> eta pi^{-} p at 18 GeV/c are given. Separate analyses for the 2 gamma and
pi+ pi- pi0 decay modes of the eta are presented. An amplitude analysis of the
data indicates the presence of interference between the a(2)(1320)- and a
J^{PC}=1^{-+} wave between 1.2 and 1.6 GeV/c^2. The phase difference between
these waves shows phase motion not attributable solely to the a(2)(1320)-. The
data can be fitted by interference between the a(2)(1320)- and an exotic 1^{-+}
resonance with M = 1370 +-16 +50 -30} MeV/c^2 and Gamma = 385 +- 40 +65 -105
MeV/c^2. Our results are compared with those of other experiments.Comment: 50 pages of text and 34 figure
The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record
the images and spectra of celestial X-ray sources focused by the three X-ray
mirrors. There is one camera at the focus of each mirror; two of the cameras
contain seven MOS CCDs, while the third uses twelve PN CCDs, defining a
circular field of view of 30 arcmin diameter in each case. The CCDs were
specially developed for EPIC, and combine high quality imaging with spectral
resolution close to the Fano limit. A filter wheel carrying three kinds of
X-ray transparent light blocking filter, a fully closed, and a fully open
position, is fitted to each EPIC instrument. The CCDs are cooled passively and
are under full closed loop thermal control. A radio-active source is fitted for
internal calibration. Data are processed on-board to save telemetry by removing
cosmic ray tracks, and generating X-ray event files; a variety of different
instrument modes are available to increase the dynamic range of the instrument
and to enable fast timing. The instruments were calibrated using laboratory
X-ray beams, and synchrotron generated monochromatic X-ray beams before launch;
in-orbit calibration makes use of a variety of celestial X-ray targets. The
current calibration is better than 10% over the entire energy range of 0.2 to
10 keV. All three instruments survived launch and are performing nominally in
orbit. In particular full field-of-view coverage is available, all electronic
modes work, and the energy resolution is close to pre-launch values. Radiation
damage is well within pre-launch predictions and does not yet impact on the
energy resolution. The scientific results from EPIC amply fulfil pre-launch
expectations.Comment: 9 pages, 11 figures, accepted for publication in the A&A Special
Issue on XMM-Newto
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
Search for charginos in e+e- interactions at sqrt(s) = 189 GeV
An update of the searches for charginos and gravitinos is presented, based on
a data sample corresponding to the 158 pb^{-1} recorded by the DELPHI detector
in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was
found. The lower mass limits are 4-5 GeV/c^2 higher than those obtained at a
centre-of-mass energy of 183 GeV. The (\mu,M_2) MSSM domain excluded by
combining the chargino searches with neutralino searches at the Z resonance
implies a limit on the mass of the lightest neutralino which, for a heavy
sneutrino, is constrained to be above 31.0 GeV/c^2 for tan(beta) \geq 1.Comment: 22 pages, 8 figure
Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP
Promptly decaying lightest neutralinos and long-lived staus are searched for
in the context of light gravitino scenarios. It is assumed that the stau is the
next to lightest supersymmetric particle (NLSP) and that the lightest
neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector
at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of
the production of these particles is found. Hence, lower mass limits for both
kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is
found to be greater than 71.5 GeV/c^2. In the search for long-lived stau,
masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10
to 150 \eVcc . Combining this search with the searches for stable heavy leptons
and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc
may be set for the stau mas
Hadronization properties of b quarks compared to light quarks in e+e- -> q qbar from 183 to 200 GeV
The DELPHI detector at LEP has collected 54 pb^{-1} of data at a
centre-of-mass energy around 183 GeV during 1997, 158 pb^{-1} around 189 GeV
during 1998, and 187 pb^{-1} between 192 and 200 GeV during 1999. These data
were used to measure the average charged particle multiplicity in e+e- -> b
bbar events, _{bb}, and the difference delta_{bl} between _{bb} and the
multiplicity, _{ll}, in generic light quark (u,d,s) events: delta_{bl}(183
GeV) = 4.55 +/- 1.31 (stat) +/- 0.73 (syst) delta_{bl}(189 GeV) = 4.43 +/- 0.85
(stat) +/- 0.61 (syst) delta_{bl}(200 GeV) = 3.39 +/- 0.89 (stat) +/- 1.01
(syst). This result is consistent with QCD predictions, while it is
inconsistent with calculations assuming that the multiplicity accompanying the
decay of a heavy quark is independent of the mass of the quark itself.Comment: 13 pages, 2 figure
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