17,333 research outputs found
Phase metrology with multi-cycle two-colour pulses
Strong-field phenomena driven by an intense infrared (IR) laser depend on
during what part of the field cycle they are initiated. By changing the
sub-cycle character of the laser electric field it is possible to control such
phenomena. For long pulses, sub-cycle shaping of the field can be done by
adding a relatively weak, second harmonic of the driving field to the pulse.
Through constructive and destructive interference, the combination of strong
and weak fields can be used to change the probability of a strong-field process
being initiated at any given part of the cycle. In order to control sub-cycle
phenomena with optimal accuracy, it is necessary to know the phase difference
of the strong and the weak fields precisely. If the weaker field is an even
harmonic of the driving field, electrons ionized by the field will be
asymmetrically distributed between the positive and negative directions of the
combined fields. Information about the asymmetry can yield information about
the phase difference. A technique to measure asymmetry for few-cycle pulses,
called Stereo-ATI (Above Threshold Ionization), has been developed by [Paulus G
G, et al 2003 Phys. Rev. Lett. 91]. This paper outlines an extension of this
method to measure the phase difference between a strong IR and its second
harmonic
Reduced phase error through optimized control of a superconducting qubit
Minimizing phase and other errors in experimental quantum gates allows higher
fidelity quantum processing. To quantify and correct for phase errors in
particular, we have developed a new experimental metrology --- amplified phase
error (APE) pulses --- that amplifies and helps identify phase errors in
general multi-level qubit architectures. In order to correct for both phase and
amplitude errors specific to virtual transitions and leakage outside of the
qubit manifold, we implement "half derivative" an experimental simplification
of derivative reduction by adiabatic gate (DRAG) control theory. The phase
errors are lowered by about a factor of five using this method to per gate, and can be tuned to zero. Leakage outside the qubit
manifold, to the qubit state, is also reduced to for
faster gates.Comment: 4 pages, 4 figures with 2 page supplementa
Waveform Approach for Assessing Conformity of CISPR 16-1-1 Measuring Receivers
An alternative approach for assessing the conformity of electromagnetic interference measuring receivers with respect to the baseline CISPR 16-1-1 requirements is proposed. The method’s core is based on the generation of digitally synthesized complex waveforms comprising multisine excitation signals and modulated pulses. The superposition of multiple narrowband reference signals populating the standard frequency bands allows for a single-stage evaluation of the receiver’s voltage accuracy and frequency selectivity. Moreover, characterizing the response of the weighting detectors using modulated pulses is more repeatable and less restrictive than the conventional approach. This methodology significantly reduces the amount of time required to complete the verification of the receiver’s baseline magnitudes, because time-domain measurements enable a broadband assessment while the typical calibration methodology follows the time-consuming narrow band frequency sweep scheme. Since the reference signals are generated using arbitrary waveform generators, they can be easily reproduced from a standard numerical vector. For different test receivers, the results of such assessment are presented in the 9 kHz–1 GHz frequency range. Finally, a discussion on the measurement uncertainty of this methodology for assessing measuring receivers is given.Postprint (author's final draft
Quantum-limited metrology and Bose-Einstein condensates
We discuss a quantum-metrology protocol designed to estimate a physical
parameter in a Bose-Einstein condensate of N atoms, and we show that the
measurement uncertainty can decrease faster than 1/N. The 1/N scaling is
usually thought to be the best possible in any measurement scheme. From the
perspective of quantum information theory, we outline the main idea that leads
to a measurement uncertainty that scales better than 1/N. We examine in detail
some potential problems and challenges that arise in implementing such a
measurement protocol using a Bose-Einstein condensate. We discuss how some of
these issues can be dealt with by using lower-dimensional condensates trapped
in nonharmonic potentials.Comment: 32 pages, 1 figure, updated reference
Differential Evolution for Many-Particle Adaptive Quantum Metrology
We devise powerful algorithms based on differential evolution for adaptive
many-particle quantum metrology. Our new approach delivers adaptive quantum
metrology policies for feedback control that are orders-of-magnitude more
efficient and surpass the few-dozen-particle limitation arising in methods
based on particle-swarm optimization. We apply our method to the
binary-decision-tree model for quantum-enhanced phase estimation as well as to
a new problem: a decision tree for adaptive estimation of the unknown bias of a
quantum coin in a quantum walk and show how this latter case can be realized
experimentally.Comment: Fig. 2(a) is the cover of Physical Review Letters Vol. 110 Issue 2
Quantum Metrology with Cold Atoms
Quantum metrology is the science that aims to achieve precision measurements
by making use of quantum principles. Attribute to the well-developed techniques
of manipulating and detecting cold atoms, cold atomic systems provide an
excellent platform for implementing precision quantum metrology. In this
chapter, we review the general procedures of quantum metrology and some
experimental progresses in quantum metrology with cold atoms. Firstly, we give
the general framework of quantum metrology and the calculation of quantum
Fisher information, which is the core of quantum parameter estimation. Then, we
introduce the quantum interferometry with single and multiparticle states. In
particular, for some typical multiparticle states, we analyze their ultimate
precision limits and show how quantum entanglement could enhance the
measurement precision beyond the standard quantum limit. Further, we review
some experimental progresses in quantum metrology with cold atomic systems.Comment: 53 pages, 9 figures, revised versio
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