1,860 research outputs found
High-fidelity trapped-ion quantum logic using near-field microwaves
We demonstrate a two-qubit logic gate driven by near-field microwaves in a
room-temperature microfabricated ion trap. We measure a gate fidelity of
99.7(1)\%, which is above the minimum threshold required for fault-tolerant
quantum computing. The gate is applied directly to Ca "atomic clock"
qubits (coherence time ) using the microwave
magnetic field gradient produced by a trap electrode. We introduce a
dynamically-decoupled gate method, which stabilizes the qubits against
fluctuating a.c.\ Zeeman shifts and avoids the need to null the microwave
field
Optical sampling and metrology using a soliton-effect compression pulse source
A low jitter optical pulse source for applications including optical sampling and optical
metrology was modelled and then experimentally implemented using photonic
components. Dispersion and non-linear fibre effects were utilised to compress a periodic
optical waveform to generate pulses of the order of 10 picoseconds duration, via
soliton-effect compression. Attractive features of this pulse source include electronically
tuneable repetition rates greater than 1.5 GHz, ultra-short pulse duration (10-15 ps), and
low timing jitter as measured by both harmonic analysis and single-sideband (SSB)
phase noise measurements. The experimental implementation of the modelled
compression scheme is discussed, including the successful removal of stimulated
Brillouin scattering (SBS) through linewidth broadening by injection dithering or phase
modulation. Timing jitter analysis identifies many unwanted artefacts generated by the
SBS suppression methods, hence an experimental arrangement is devised (and was
subsequently patented) which ensures that there are no phase modulation spikes present
on the SSB phase noise spectrum over the offset range of interest for optical sampling
applications, 10Hz-Nyquist. It is believed that this is the first detailed timing jitter study
of a soliton-effect compression scheme. The soliton-effect compression pulses are then
used to perform what is believed to be the first demonstration of optical sampling using
this type of pulse source.
The pulse source was also optimised for use in a novel optical metrology (range
finding) system, which is being developed and patented under European Space Agency
funding as an enabling technology for formation flying satellite missions. This new
approach to optical metrology, known as Scanning Interferometric Pulse Overlap
Detection (SIPOD), is based on scanning the optical pulse repetition rate to find the
specific frequencies which allow the return pulses from the outlying satellite, i.e. the
measurement arm, to overlap exactly with a reference pulse set on the hub satellite. By
superimposing a low frequency phase modulation onto the optical pulse train, it is
possible to detect the pulse overlap condition using conventional heterodyne detection.
By rapidly scanning the pulse repetition rate to find two frequencies which provide the
overlapping pulse condition, high precision optical pulses can be used to provide high
resolution unambiguous range information, using only relatively simple electronic detection circuitry. SIPOD’s maximum longitudinal range measurement is limited only
by the coherence length of the laser, which can be many tens of kilometres. Range
measurements have been made to better than 10 microns resolution over extended
duration trial periods, at measurement update rates of up to 470 Hz. This system is
currently scheduled to fly on ESA’s PROBA-3 mission in 2012 to measure the intersatellite
spacing for a two satellite coronagraph instrument.
In summary, this thesis is believed to present three novel areas of research: the first
detailed jitter characterisation of a soliton-effect compression source, the first optical
sampling using such a compression source, and a novel optical metrology range finding
system, known as SIPOD, which utilises the tuneable repetition rate and highly stable
nature of the compression source pulses
Participation of Bell Telephone Laboratories in Project Echo and Experimental Results
On August 12, 1960, Echo I, a 100-foot-diameter spherical balloon, was placed in orbit around the earth by the National Aeronautics and Space Administration. The objective was to demonstrate the feasibility of long-distance communication by microwave reflection from a satellite. A two-way coast-to-coast voice circuit was to be established between the Jet Propulsion Laboratory (JPL) facility in California and a station provided by Bell Telephone Laboratories (STL) in New Jersey. Similar tests were also planned with the Naval Research Laboratory and other stations. This paper describes the general organization and operation of the Holmdel, New Jersey, station, and discusses the results of the experiments performed between the balloon launching and March 1, 1961. Successful voice communication was achieved through a variety of modulation methods including frequency modulation with feedback, amplitude modulation, single-sideband modulation, and narrow-band phase modulation. Careful measurements were also made of the loss in the transmission path
A dual-polarized quasi-optical SIS mixer at 550 GHz
In this paper, we describe the design, fabrication, and the performance of a low-noise dual-polarized quasi-optical superconductor-insulator-superconductor (SIS) mixer at 550 GHz. The mixer utilizes a novel cross-slot antenna on a hyperhemispherical substrate lens, two junction tuning circuits, niobium trilayer junctions, and an IF circuit containing a lumped element 180° hybrid. The antenna consists of an orthogonal pair of twin-slot antennas, and has four feed points, two for each polarization. Each feed point is coupled to a two-junction SIS mixer. The 180° IF hybrid is implemented using a lumped element/microstrip circuit located inside the mixer block. Fourier transform spectrometer measurements of the mixer frequency response show good agreement with computer simulations. The measured co-polarized and cross-polarized patterns for both polarizations also agree with the theoretical predictions. The noise performance of the dual-polarized mixer is excellent giving uncorrected receiver noise temperature of better than 115 K (double sideband) at 528 GHz for both the polarizations
Meteorological satellites
An overview is presented of the meteorological satellite programs that have been evolving from 1958 to the present, and plans for the future meteorological and environmental satellite systems that are scheduled to be placed into service in the early 1980's are reviewed. The development of the TIROS family of weather satellites, including TIROS, ESSA, ITOS/NOAA, and the present TIROS-N (the third generation operational system) is summarized. The contribution of the Nimbus and ATS technology satellites to the development of the operational-orbiting and geostationary satellites is discussed. Included are descriptions of both the TIROS-N and the DMSP payloads currently under development to assure a continued and orderly growth of these systems into the 1980's
Digital electronic predistortion for optical communications
The distortion of optical signals has long been an issue limiting the performance of
communication systems. With the increase of transmission speeds the effects of distortion
are becoming more prominent. Because of this, the use of methods known from digital
signal processing (DSP) are being introduced to compensate for them.
Applying DSP to improve optical signals has been limited by a discrepancy in digital signal
processing speeds and optical transmission speeds. However high speed Field
Programmable Gate Arrays (FPGA) which are sufficiently fast have now become available
making DSP experiments without costly ASIC implementation possible for optical
transmission experiments.
This thesis focuses on Look Up Table (LUT) based digital Electronic Predistortion (EPD) for
optical transmission. Because it is only one out of many possible implementations of EPD,
it has to be placed in context with other EPD techniques and other distortion combating
techniques in general, especially since it is possible to combine the different techniques.
Building an actual transmitter means that compromises and decisions have to be made in
the design and implementation of an EPD based system. These are based on balancing the
desire to achieve optimal performance with technological and economic limitations. This
is partly done using optical simulations to asses the performance.
This thesis describes a novel experimental transmitter that has been built as part of this
research applying LUT based EPD to an optical signal. The experimental transmitter
consists of a digital design (using a hardware description language) for a pair of FPGAs and
an analogue optical/electronic setup including two standard DAC integrated circuits. The
DSP in the transmitter compensated for both chromatic dispersion and self phase
modulation.
We achieved transmission of 10.7 Gb/s non-return-to-zero (NRZ) signals with a +4 dBm
launch power over 450 km keeping the required optical-signal-to-noise-ratio (OSNR) for a
bit-error-rate of 2x10^{-3} below 11 dB. In doing so we showed experimentally, for the first
time, that nonlinear effects can be compensated with this approach and that the
combination of FPGA-DAC is a viable approach for an experimental setup
HARP/ACSIS: A submillimetre spectral imaging system on the James Clerk Maxwell Telescope
This paper describes a new Heterodyne Array Receiver Programme (HARP) and
Auto-Correlation Spectral Imaging System (ACSIS) that have recently been
installed and commissioned on the James Clerk Maxwell Telescope (JCMT). The
16-element focal-plane array receiver, operating in the submillimetre from 325
to 375 GHz, offers high (three-dimensional) mapping speeds, along with
significant improvements over single-detector counterparts in calibration and
image quality. Receiver temperatures are 120 K across the whole band and
system temperatures of 300K are reached routinely under good weather
conditions. The system includes a single-sideband filter so these are SSB
figures. Used in conjunction with ACSIS, the system can produce large-scale
maps rapidly, in one or more frequency settings, at high spatial and spectral
resolution. Fully-sampled maps of size 1 square degree can be observed in under
1 hour.
The scientific need for array receivers arises from the requirement for
programmes to study samples of objects of statistically significant size, in
large-scale unbiased surveys of galactic and extra-galactic regions. Along with
morphological information, the new spectral imaging system can be used to study
the physical and chemical properties of regions of interest. Its
three-dimensional imaging capabilities are critical for research into
turbulence and dynamics. In addition, HARP/ACSIS will provide highly
complementary science programmes to wide-field continuum studies, and produce
the essential preparatory work for submillimetre interferometers such as the
SMA and ALMA.Comment: MNRAS Accepted 2009 July 2. 18 pages, 25 figures and 6 table
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