363 research outputs found
Extending the memory times of trapped-ion qubits with error correction and global entangling operations
The technical demands to perform quantum error correction are considerable.
The task requires the preparation of a many-body entangled state, together with
the ability to make parity measurements over subsets of the physical qubits of
the system to detect errors. Here we propose two trapped-ion experiments to
realise error-correcting codes of variable size to protect a single encoded
qubit from dephasing errors. Novel to our schemes is the use of a global
entangling phase gate, which could be implemented in both Penning traps and
Paul traps. We make use of this entangling operation to significantly reduce
the experimental complexity of state preparation and syndrome measurements. We
also show, in our second scheme, that storage times can be increased further by
repeatedly teleporting the logical information between two codes supported by
the same ion Coulomb crystal to learn information about the locations of
errors. We estimate that a logical qubit encoded in such a crystal will
maintain high coherence for times more than an order of magnitude longer than
each physical qubit would.Comment: 18 pages, 8 figures. The authors list has changed since the first
version of this draf
Trapped-ion quantum error-correcting protocols using only global operations
Quantum error-correcting codes are many-body entangled states that are
prepared and measured using complex sequences of entangling operations. Each
element of such an entangling sequence introduces noise to delicate quantum
information during the encoding or reading out of the code. It is important
therefore to find efficient entangling protocols to avoid the loss of
information. Here we propose an experiment that uses only global entangling
operations to encode an arbitrary logical qubit to either the five-qubit
repetition code or the five-qubit code, with a six-ion Coulomb crystal
architecture in a Penning trap. We show that the use of global operations
enables us to prepare and read out these codes using only six and ten global
entangling pulses, respectively. The proposed experiment also allows the
acquisition of syndrome information during readout. We provide a noise analysis
for the presented protocols, estimating that we can achieve a six-fold
improvement in coherence time with noise as high as on each
entangling operation.Comment: 7 pages, 4 figures, published version, comments are welcom
A short response-time atomic source for trapped ion experiments
Ion traps are often loaded from atomic beams produced by resistively heated
ovens. We demonstrate an atomic oven which has been designed for fast control
of the atomic flux density and reproducible construction. We study the limiting
time constants of the system and, in tests with , show we can
reach the desired level of flux in 12s, with no overshoot. Our results indicate
that it may be possible to achieve an even faster response by applying an
appropriate one-off heat treatment to the oven before it is used.Comment: 5 pages, 7 figure
Effects of cavity birefringence in polarisation-encoded quantum networks
The generation of entanglement between distant atoms via single photons is
the basis for networked quantum computing, a promising route to large-scale
trapped-ion and trapped-atom processors. Locating the emitter within an optical
cavity provides an efficient matter-light interface, but mirror-induced
birefringence within the cavity introduces time-dependence to the polarisation
of the photons produced. We show that such `polarisation oscillation' effects
can lead to severe loss of fidelity in the context of two-photon, polarisation
encoded measurement-based remote entanglement schemes. It is always preferable
to suppress these errors at source by minimising mirror ellipticity, but we
propose two remedies for systems where this cannot be achieved. We conclude
that even modest cavity birefringence can be detrimental to remote entanglement
performance, to an extent that may limit the suitability of
polarisation-encoded schemes for large-scale quantum networks.Comment: 18 pages, 8 figure
An optically-heated atomic source for compact ion trap vacuum systems
We present a design for an atomic oven suitable for loading ion traps, which
is operated via optical heating with a continuous-wave multimode diode laser.
The absence of the low-resistance electrical connections necessary for Joule
heating allows the oven to be extremely well thermally isolated from the rest
of the vacuum system, and for an oven filled with calcium we achieve a number
density suitable for rapid ion loading in the target region with ~200 mW of
laser power, limited by radiative losses. With simple feedforward to the laser
power, the turn-on time for the oven is less than 20 s, while the oven contains
enough calcium to operate continuously for many thousands of years without
replenishment.Comment: 7 pages, 5 figure
Mode mixing and losses in misaligned microcavities
We present a study on the optical losses of Fabry-P\'erot cavities subject to
realistic transverse mirror misalignment. We consider mirrors of the two most
prevalent surface forms: idealised spherical depressions, and Gaussian profiles
generated by laser ablation. We first describe the mode mixing phenomena seen
in the spherical mirror case and compare to the frequently-used clipping model,
observing close agreement in the predicted diffraction loss, but with the
addition of protective mode mixing at transverse degeneracies. We then discuss
the Gaussian mirror case, detailing how the varying surface curvature across
the mirror leads to complex variations in round trip loss and mode profile. In
light of the severe mode distortion and strongly elevated loss predicted for
many cavity lengths and transverse alignments when using Gaussian mirrors, we
suggest that the consequences of mirror surface profile are carefully
considered when designing cavity experiments.Comment: 16 pages, 12 figure
Efficient operator method for modelling mode mixing in misaligned optical cavities
The transverse field structure and diffraction loss of the resonant modes of
Fabry-P\'erot optical cavities are acutely sensitive to the alignment and shape
of the mirror substrates. We develop extensions to the `mode mixing' method
applicable to arbitrary mirror shapes, which both facilitate fast calculation
of the modes of cavities with transversely misaligned mirrors and enable the
determination and transformation of the geometric properties of these modes. We
show how these methods extend previous capabilities by including the
practically-motivated case of transverse mirror misalignment, unveiling rich
and complex structure of the resonant modes.Comment: 17 pages, 7 figure
Optimisation of Scalable Ion-Cavity Interfaces for Quantum Photonic Networks
In the design optimisation of ion-cavity interfaces for quantum networking
applications, difficulties occur due to the many competing figures of merit and
highly interdependent design constraints, many of which present `soft-limits',
amenable to improvement at the cost of engineering time. In this work we
present a systematic approach to this problem which offers a means to identify
efficient and robust operating regimes, and to elucidate the trade-offs
involved in the design process, allowing engineering efforts to be focused on
the most sensitive and critical parameters. We show that in many relevant cases
it is possible to approximately separate the geometric aspects of the
cooperativity from those associated with the atomic system and the mirror
surfaces themselves, greatly simplifying the optimisation procedure. Although
our approach to optimisation can be applied to most operating regimes, here we
consider cavities suitable for typical ion trapping experiments, and with
substantial transverse misalignment of the mirrors. We find that cavities with
mirror misalignments of many micrometres can still offer very high photon
extraction efficiencies, offering an appealing route to the scalable production
of ion-cavity interfaces for large scale quantum networks
The orbit structure of Dynkin curves
Let G be a simple algebraic group over an algebraically closed field k;
assume that Char k is zero or good for G. Let \cB be the variety of Borel
subgroups of G and let e in Lie G be nilpotent. There is a natural action of
the centralizer C_G(e) of e in G on the Springer fibre \cB_e = {B' in \cB | e
in Lie B'} associated to e. In this paper we consider the case, where e lies in
the subregular nilpotent orbit; in this case \cB_e is a Dynkin curve. We give a
complete description of the C_G(e)-orbits in \cB_e. In particular, we classify
the irreducible components of \cB_e on which C_G(e) acts with finitely many
orbits. In an application we obtain a classification of all subregular orbital
varieties admitting a finite number of B-orbits for B a fixed Borel subgroup of
G.Comment: 12 pages, to appear in Math
The Grizzly, October 17, 1986
False Alarm Alarms Dean and 310 Party. LCB Suspected • Two Alumnae Tell Pros and Cons of Pledging • Electrical Accident Victims Doing Well Considering the Extent of Their Injuries • Editorial: Temple Jars Campus • Letters: Alumna Gives New Interpretation of Temple; Incarcerated in Attica • Commitment to Excellence Results in Tuition Hike • $37,000 Available • Genesis Returns Home and Turns it on Again • Despite Comeback, Bears Are Tied Up • Bear Pack Overcomes Doubt in March to Top • Up and Down Season for Injured Bears • Athlete of the Week • Selling to Recruitershttps://digitalcommons.ursinus.edu/grizzlynews/1172/thumbnail.jp
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