2,314 research outputs found
Demonstration of a quantum logic gate in a cryogenic surface-electrode ion trap
We demonstrate quantum control techniques for a single trapped ion in a
cryogenic, surface-electrode trap. A narrow optical transition of Sr+ along
with the ground and first excited motional states of the harmonic trapping
potential form a two-qubit system. The optical qubit transition is susceptible
to magnetic field fluctuations, which we stabilize with a simple and compact
method using superconducting rings. Decoherence of the motional qubit is
suppressed by the cryogenic environment. AC Stark shift correction is
accomplished by controlling the laser phase in the pulse sequencer, eliminating
the need for an additional laser. Quantum process tomography is implemented on
atomic and motional states using conditional pulse sequences. With these
techniques we demonstrate a Cirac-Zoller Controlled-NOT gate in a single ion
with a mean fidelity of 91(1)%.Comment: 11 pages, 5 figures, 4 table
Laser-induced charging of microfabricated ion traps
Electrical charging of metal surfaces due to photoelectric generation of
carriers is of concern in trapped ion quantum computation systems, due to the
high sensitivity of the ions' motional quantum states to deformation of the
trapping potential. The charging induced by typical laser frequencies involved
in doppler cooling and quantum control is studied here, with microfabricated
surface electrode traps made of aluminum, copper, and gold, operated at 6 K
with a single Sr ion trapped 100 m above the trap surface. The lasers
used are at 370, 405, 460, and 674 nm, and the typical photon flux at the trap
is 10 photons/cm/sec. Charging is detected by monitoring the ion's
micromotion signal, which is related to the number of charges created on the
trap. A wavelength and material dependence of the charging behavior is
observed: lasers at lower wavelengths cause more charging, and aluminum
exhibits more charging than copper or gold. We describe the charging dynamic
based on a rate equation approach.Comment: 8 pages, 8 figure
Superconducting microfabricated ion traps
We fabricate superconducting ion traps with niobium and niobium nitride and
trap single 88Sr ions at cryogenic temperatures. The superconducting transition
is verified and characterized by measuring the resistance and critical current
using a 4-wire measurement on the trap structure, and observing change in the
rf reflection. The lowest observed heating rate is 2.1(3) quanta/sec at 800 kHz
at 6 K and shows no significant change across the superconducting transition,
suggesting that anomalous heating is primarily caused by noise sources on the
surface. This demonstration of superconducting ion traps opens up possibilities
for integrating trapped ions and molecular ions with superconducting devices.Comment: 3 pages, 2 figure
Individual addressing of ions using magnetic field gradients in a surface-electrode ion trap
Dense array of ions in microfabricated traps represent one possible way to
scale up ion trap quantum computing. The ability to address individual ions is
an important component of such a scheme. We demonstrate individual addressing
of trapped ions in a microfabricated surface-electrode trap using a magnetic
field gradient generated on-chip. A frequency splitting of 310(2) kHz for two
ions separated by 5 um is achieved. Selective single qubit operations are
performed on one of two trapped ions with an average of 2.2+/-1.0% crosstalk.
Coherence time as measured by the spin-echo technique is unaffected by the
field gradient.Comment: 3 pages, 3 figures; submitted to AP
A microfabricated surface ion trap on a high-finesse optical mirror
A novel approach to optics integration in ion traps is demonstrated based on
a surface electrode ion trap that is microfabricated on top of a dielectric
mirror. Additional optical losses due to fabrication are found to be as low as
80 ppm for light at 422 nm. The integrated mirror is used to demonstrate light
collection from, and imaging of, a single 88 Sr+ ion trapped m
above the mirror.Comment: 4 pages, 3 figure
Temperature Dependence of Electric Field Noise Above Gold Surfaces
Electric field noise from fluctuating patch potentials is a significant
problem for a broad range of precision experiments, including trapped ion
quantum computation and single spin detection. Recent results demonstrated
strong suppression of this noise by cryogenic cooling, suggesting an underlying
thermal process. We present measurements characterizing the temperature and
frequency dependence of the noise from 7 to 100 K, using a single Sr+ ion
trapped 75 um above the surface of a gold plated surface electrode ion trap.
The noise amplitude is observed to have an approximate 1/f spectrum around 1
MHz, and grows rapidly with temperature as T^beta for beta from 2 to 4. The
data are consistent with microfabricated cantilever measurements of non-contact
friction but do not extrapolate to the DC measurements with neutral atoms or
contact potential probes.Comment: 4 pages, 3 figures, 1 tabl
Charge variants characterization and release assay development for co-formulated antibodies as a combination therapy
© 2019, © 2019 The Author(s). Published with license by Taylor & Francis Group, LLC. Combination therapy is a fast-growing strategy to maximize therapeutic benefits to patients. Co-formulation of two or more therapeutic proteins has advantages over the administration of multiple medications, including reduced medication errors and convenience for patients. Characterization of co-formulated biologics can be challenging due to the high degree of similarity in the physicochemical properties of co-formulated proteins, especially at different concentrations of individual components. We present the results of a deamidation study of one monoclonal antibody component (mAb-B) in co-formulated combination antibodies (referred to as COMBO) that contain various ratios of mAb-A and mAb-B. A single deamidation site in the complementarity-determining region of mAb-B was identified as a critical quality attribute (CQA) due to its impact on biological activity. A conventional charge-based method of monitoring mAb-B deamidation presented specificity and robustness challenges, especially when mAb-B was a minor component in the COMBO, making it unsuitable for lot release and stability testing. We developed and qualified a new, quality-control-friendly, single quadrupole Dalton mass detector (QDa)–based method to monitor site-specific deamidation. Our approach can be also used as a multi-attribute method for monitoring other quality attributes in COMBO. This analytical paradigm is applicable to the identification of CQAs in combination therapeutic molecules, and to the subsequent development of a highly specific, highly sensitive, and sufficiently robust method for routine monitoring CQAs for lot release test and during stability studies
Timing analysis for 20 millisecond pulsars in the Parkes Pulsar Timing Array
We present timing models for 20 millisecond pulsars in the Parkes Pulsar
Timing Array. The precision of the parameter measurements in these models has
been improved over earlier results by using longer data sets and modelling the
non-stationary noise. We describe a new noise modelling procedure and
demonstrate its effectiveness using simulated data. Our methodology includes
the addition of annual dispersion measure (DM) variations to the timing models
of some pulsars. We present the first significant parallax measurements for
PSRs J1024-0719, J1045-4509, J1600-3053, J1603-7202, and J1730-2304, as well as
the first significant measurements of some post-Keplerian orbital parameters in
six binary pulsars, caused by kinematic effects. Improved Shapiro delay
measurements have resulted in much improved pulsar mass measurements,
particularly for PSRs J0437-4715 and J1909-3744 with
and respectively. The improved orbital
period-derivative measurement for PSR J0437-4715 results in a derived distance
measurement at the 0.16% level of precision, pc, one of the
most fractionally precise distance measurements of any star to date.Comment: 21 pages, 5 figures, 7 tables. Accepted for publication in MNRA
Structural and dielectric properties of SrTiO from first principles
We have investigated the structural and dielectric properties of
SrTiO,the first member of the SrTiO
Ruddlesden-Popper series, within density functional theory. Motivated by recent
work in which thin films of SrTiO were grown by molecular beam
epitaxy (MBE) on SrTiO substrates, the in-plane lattice parameter was
fixed to the theoretically optimized lattice constant of cubic SrTiO
(n=), while the out-of-plane lattice parameter and the internal
structural parameters were relaxed. The fully relaxed structure was also
investigated. Density functional perturbation theory was used to calculate the
zone-center phonon frequencies, Born effective charges, and the electronic
dielectric permittivity tensor. A detailed study of the contribution of
individual infrared-active modes to the static dielectric permittivity tensor
was performed. The calculated Raman and infrared phonon frequencies were found
to be in agreement with experiment where available. Comparisons of the
calculated static dielectric permittivity with experiments on both ceramic
powders and epitaxial thin films are discussed.Comment: 11 pages, 1 figure, 8 tables, submitted to Phys. Rev.
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