66 research outputs found
Fibre-optic delivery of time and frequency to VLBI station
The quality of Very Long Baseline Interferometry (VLBI) radio observations
predominantly relies on precise and ultra-stable time and frequency (T&F)
standards, usually hydrogen masers (HM), maintained locally at each VLBI
station. Here, we present an operational solution in which the VLBI
observations are routinely carried out without use of a local HM, but using
remote synchronization via a stabilized, long-distance fibre-optic link. The
T&F reference signals, traceable to international atomic timescale (TAI), are
delivered to the VLBI station from a dedicated timekeeping laboratory.
Moreover, we describe a proof-of-concept experiment where the VLBI station is
synchronized to a remote strontium optical lattice clock during the
observation.Comment: 8 pages, 8 figures, matches the version published in A&A, section
Astronomical instrumentatio
Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second
We present a system of two independent strontium optical lattice standards
probed with a single shared ultra-narrow laser. The absolute frequency of the
clocks can be verified by the use of Er:fiber optical frequency comb with the
GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of
the clock line and measurements of frequency stability of the two strontium
optical lattice clocks.Comment: This is an author-created, un-copyedited version of an article
accepted for publication in Meas. Sci. Technol. The publisher is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The Version of Record is available online at
doi:10.1088/0957-0233/26/7/07520
Deformed Heisenberg algebra and minimal length
A one-dimensional deformed Heisenberg algebra is studied. We
answer the question: For what function of deformation there exists a
nonzero minimal uncertainty in position (minimal length). We also find an
explicit expression for the minimal length in the case of arbitrary function of
deformation.Comment: to be published in JP
Line shape measurements of rubidium 5S-7S two-photon transition
We report the use of a digital lock to measure the line profile and center frequency of rubidium 5S-7S two-photon transitions with a cw laser referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm), insensitive to first-order in a magnetic field, is a promising candidate for frequency reference
Topological insulator and quantum memory
Measurements done on the quantum systems are too specific. Contrary to their
classical counterparts, quantum measurements can be invasive and destroy the
state of interest. Besides, quantumness limits the accuracy of measurements
done on quantum systems. Uncertainty relations define the universal accuracy
limit of the quantum measurements. Relatively recently, it was discovered that
quantum correlations and quantum memory might reduce the uncertainty of quantum
measurements. In the present work, we study two different types of measurements
done on the topological system. Namely, we discuss measurements done on the
spin operators and the canonical pair of operators: momentum and coordinate. We
quantify the spin operator's measurements through the entropic measures of
uncertainty and exploit the concept of quantum memory. While for the momentum
and coordinate operators, we exploit the improved uncertainty relations. We
discovered that quantum memory reduces the uncertainties of spin measurements.
On the hand, we proved that the uncertainties in the measurements of the
coordinate and momentum operators depend on the value of the momentum and are
substantially enhanced at small distances between itinerant and localized
electrons (the large momentum limit). We note that the topological nature of
the system leads to the spin-momentum locking. The momentum of the electron
depends on the spin and vice versa. Therefore, we suggest the indirect
measurement scheme for the momentum and coordinate operators through the spin
operator. Due to the factor of quantum memory, such indirect measurements in
topological insulators have smaller uncertainties rather than direct
measurements
Large-momentum convergence of Hamiltonian bound-state dynamics of effective fermions in quantum field theory
Contributions to the bound-state dynamics of fermions in local quantum field
theory from the region of large relative momenta of the constituent particles,
are studied and compared in two different approaches. The first approach is
conventionally developed in terms of bare fermions, a Tamm-Dancoff truncation
on the particle number, and a momentum-space cutoff that requires counterterms
in the Fock-space Hamiltonian. The second approach to the same theory deals
with bound states of effective fermions, the latter being derived from a
suitable renormalization group procedure. An example of two-fermion bound
states in Yukawa theory, quantized in the light-front form of dynamics, is
discussed in detail. The large-momentum region leads to a buildup of
overlapping divergences in the bare Tamm-Dancoff approach, while the effective
two-fermion dynamics is little influenced by the large-momentum region. This is
illustrated by numerical estimates of the large-momentum contributions for
coupling constants on the order of between 0.01 and 1, which is relevant for
quarks.Comment: 22 pages, 9 figure
- …