246 research outputs found
Quantum gate using qubit states separated by terahertz
A two-qubit quantum gate is realized using electronic excited states in a
single ion with an energy separation on the order of a terahertz times the
Planck constant as a qubit. Two phase locked lasers are used to excite a
stimulated Raman transition between two metastable states and
separated by 1.82 THz in a single trapped Ca ion to
construct a qubit, which is used as the target bit for the Cirac-Zoller
two-qubit controlled NOT gate. Quantum dynamics conditioned on a motional qubit
is clearly observed as a fringe reversal in Ramsey interferometry.Comment: 4 pages, 4 figure
Generation of Dicke states using adiabatic passage
Entangled states of two ions are realized by using an adiabatic process.
Based on the proposal by Linington and Vitanov, we have generated Dicke states
in optical qubits of two Ca ions by applying frequency-chirped
optical pulses with time-dependent envelopes to perform rapid adiabatic passage
on sideband transitions. One of the biggest advantages of adiabatic approaches
is their robustness against variations in experimental parameters, which is
verified by performing experiments for different pulse widths or peak Rabi
frequencies. Fidelities exceeding 0.5, which is the threshold for inseparable
states, are obtained over wide ranges of parameter values
Duration of Star Formation in Galactic Giant Molecular Clouds. I. The Great Nebula in Carina
We present a novel infrared spectral energy distribution (SED) modeling methodology that uses likelihood-based weighting of the model fitting results to construct probabilistic Hertzsprung–Russell diagrams (pHRD) for X-ray-identified, intermediate-mass (2–8 M⊙), pre-main-sequence young stellar populations. This methodology is designed specifically for application to young stellar populations suffering strong, differential extinction (ΔA_V > 10 mag), typical of Galactic massive star-forming regions. We pilot this technique in the Carina Nebula Complex (CNC) by modeling the 1–8 μm SEDs of 2269 likely stellar members that exhibit no excess emission from circumstellar dust disks at 4.5 μm or shorter wavelengths. A subset of ~100 intermediate-mass stars in the lightly obscured Trumpler 14 and 16 clusters have available spectroscopic T_(eff), measured from the Gaia-ESO survey. We correctly identify the stellar temperature in 85% of cases, and the aggregate pHRD for all sources returns the same peak in the stellar age distribution as obtained using the spectroscopic T_(eff). The SED model parameter distributions of stellar mass and evolutionary age reveal significant variation in the duration of star formation among four large-scale stellar overdensities within the CNC and a large distributed stellar population. Star formation began ~10 Myr ago and continues to the present day, with the star formation rate peaking ≾3 Myr ago when the massive Trumpler 14 and 16 clusters formed. We make public the set of 100,000 SED models generated from standard pre-main-sequence evolutionary tracks and our custom software package for generating pHRDs and mass–age distributions from the SED fitting results
Exotic heavy-fermion superconductivity in atomically thin CeCoIn5 films
Funding: This work is supported by Grants-in-Aid for Scientific Research (KAKENHI) (Grants No. JP18H01180, No. JP18H05227, and No. JP18K03511) from Japan Society for the Promotion of Science (JSPS), and by Core Research for Evolutional Science and Technology (CREST) (Grant No. JP-MJCR19T5) from Japan Science and Technology Agency (JST).We report an in situ scanning tunneling microscopy study of atomically thin films of CeCoIn5, a d-wave heavy-fermion superconductor. Both hybridization and superconducting gaps are observed even in monolayer CeCoIn5, providing direct evidence of superconductivity of heavy quasiparticles mediated by purely two-dimensional bosonic excitations. In these atomically thin films, Tc is suppressed to nearly half of the bulk, but is similar to CeCoIn5/YbCoIn5 superlattices containing CeCoIn5 layers with the same thickness as the thin films. Remarkably, the out-of-plane upper critical field μ0Hc2⊥ at zero temperature is largely enhanced from those of bulk and superlattices. The enhanced Hc2⊥ well exceeds the Pauli and bulk orbital limits, suggesting the possible emergence of unusual superconductivity with parity mixing caused by the inversion symmetry breaking.Publisher PDFPeer reviewe
Energy-scaling of the product state distribution for three-body recombination of ultracold atoms
Three-body recombination is a chemical reaction where the collision of three
atoms leads to the formation of a diatomic molecule. In the ultracold regime it
is expected that the production rate of a molecule generally decreases with its
binding energy , however, its precise dependence and the physics governing
it have been left unclear so far. Here, we present a comprehensive experimental
and theoretical study of the energy dependency for three-body recombination of
ultracold Rb. For this, we determine production rates for molecules in a
state-to-state resolved manner, with the binding energies ranging from
0.02 to 77 GHz. We find that the formation rate approximately scales
as , where is in the vicinity of 1. The formation rate
typically varies only within a factor of two for different rotational angular
momenta of the molecular product, apart from a possible centrifugal barrier
suppression for low binding energies. In addition to numerical three-body
calculations we present a perturbative model which reveals the physical origin
of the energy scaling of the formation rate. Furthermore, we show that the
scaling law potentially holds universally for a broad range of interaction
potentials.Comment: 15 pages, 13 figure
Thermodynamics of transition to BCS-BEC crossover superconductivity in FeSeS
The BCS-BEC crossover from strongly overlapping Cooper pairs to
non-overlapping composite bosons in the strong coupling limit has been a
long-standing issue of interacting many-body fermion systems. Recently, FeSe
semimetal with hole and electron bands emerged as a high-
superconductor located in the BCS-BEC crossover regime, owing to its very small
Fermi energies. In FeSe, however, an ordinary BCS-like heat-capacity jump is
observed at , posing a fundamental question on the characteristics
of the BCS-BEC crossover. Here we report on high-resolution heat capacity,
magnetic torque, and scanning tunneling spectroscopy measurements in
FeSeS. Upon entering the tetragonal phase at , where
nematic order is suppressed, discontinuously decreases. In this
phase, highly non-mean-field behaviors consistent with BEC-like pairing are
found in the thermodynamic quantities with giant superconducting fluctuations
extending far above , implying the change of pairing nature.
Moreover, the pseudogap formation, which is expected in BCS-BEC crossover of
single-band superconductors, is not observed in the tunneling spectra. These
results illuminate highly unusual features of the superconducting states in the
crossover regime with multiband electronic structure and competing electronic
instabilities.Comment: 12 pages, 8 figure
Duration of Star Formation in Galactic Giant Molecular Clouds. I. The Great Nebula in Carina
We present a novel infrared spectral energy distribution (SED) modeling methodology that uses likelihood-based weighting of the model fitting results to construct probabilistic Hertzsprung–Russell diagrams (pHRD) for X-ray-identified, intermediate-mass (2–8 M⊙), pre-main-sequence young stellar populations. This methodology is designed specifically for application to young stellar populations suffering strong, differential extinction (ΔA_V > 10 mag), typical of Galactic massive star-forming regions. We pilot this technique in the Carina Nebula Complex (CNC) by modeling the 1–8 μm SEDs of 2269 likely stellar members that exhibit no excess emission from circumstellar dust disks at 4.5 μm or shorter wavelengths. A subset of ~100 intermediate-mass stars in the lightly obscured Trumpler 14 and 16 clusters have available spectroscopic T_(eff), measured from the Gaia-ESO survey. We correctly identify the stellar temperature in 85% of cases, and the aggregate pHRD for all sources returns the same peak in the stellar age distribution as obtained using the spectroscopic T_(eff). The SED model parameter distributions of stellar mass and evolutionary age reveal significant variation in the duration of star formation among four large-scale stellar overdensities within the CNC and a large distributed stellar population. Star formation began ~10 Myr ago and continues to the present day, with the star formation rate peaking ≾3 Myr ago when the massive Trumpler 14 and 16 clusters formed. We make public the set of 100,000 SED models generated from standard pre-main-sequence evolutionary tracks and our custom software package for generating pHRDs and mass–age distributions from the SED fitting results
High contrast experiment of an AO-free coronagraph with a checkerboard pupil mask
A high contrast coronagraph is expected to provide one of the promising ways
to directly observe extra-solar planets. We present the newest results of our
laboratory experiment investigating "rigid" coronagraph with a binary shaped
checkerboard pupil mask, which should offer a highly stable solution for
telescopes without adaptive optics (AO) for wavefront correction in space
missions. The primary aim of this work was to study the stability of the
coronagraph, and to demonstrate its performance without adaptive wavefront
correction. Estimation of both the raw contrast and the gain of the point
spread function (PSF) subtraction were needed. The limiting factor of the
contrast was also important. A binary shaped pupil mask of a checkerboard type
has been designed. The mask, consisting of an aluminum film on a glass
substrate, was manufactured using nano-fabrication techniques with electron
beam lithography. Careful evaluation of coronagraphic performance, including
PSF subtraction, was carried out in air using the developed mask. A contrast of
was achieved for the raw coronagraphic image by areal
averaging of all of the observed dark regions. Following PSF subtraction, the
contrast reached . Speckles were a major limiting factor
throughout the dark regions of both the raw image and the PSF subtracted image.
A rigid coronagraph with PSF subtraction without AO is a useful method to
achieve high contrast observations. Applications of a rigid coronagraph to a
Space Infrared telescope for Cosmology and Astrophysics (SPICA) and other
platforms are discussed.Comment: 13 pages, 6 figure
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