685 research outputs found
Reversible simulation of bipartite product Hamiltonians
Consider two quantum systems A and B interacting according to a product
Hamiltonian H = H_A x H_B. We show that any two such Hamiltonians can be used
to simulate each other reversibly (i.e., without efficiency losses) with the
help of local unitary operations and local ancillas. Accordingly, all non-local
features of a product Hamiltonian -- including the rate at which it can be used
to produce entanglement, transmit classical or quantum information, or simulate
other Hamiltonians -- depend only upon a single parameter. We identify this
parameter and use it to obtain an explicit expression for the entanglement
capacity of all product Hamiltonians. Finally, we show how the notion of
simulation leads to a natural formulation of measures of the strength of a
nonlocal Hamiltonian.Comment: 10 page
Two-way quantum communication channels
We consider communication between two parties using a bipartite quantum
operation, which constitutes the most general quantum mechanical model of
two-party communication. We primarily focus on the simultaneous forward and
backward communication of classical messages. For the case in which the two
parties share unlimited prior entanglement, we give inner and outer bounds on
the achievable rate region that generalize classical results due to Shannon. In
particular, using a protocol of Bennett, Harrow, Leung, and Smolin, we give a
one-shot expression in terms of the Holevo information for the
entanglement-assisted one-way capacity of a two-way quantum channel. As
applications, we rederive two known additivity results for one-way channel
capacities: the entanglement-assisted capacity of a general one-way channel,
and the unassisted capacity of an entanglement-breaking one-way channel.Comment: 21 pages, 3 figure
Perturbation of Retinoid Homeostasis Increases Malformation Risk in Embryos Exposed to Pregestational Diabetes
Funding. This work was supported by funding from Hong Kong Research Grants Council General Research Fund project reference 441606 and 474109 to A.S.W.S., Y.C.L., C.C.W., P.J.M. and A.J.C..Peer reviewedPostprin
Realization of quantum process tomography in NMR
Quantum process tomography is a procedure by which the unknown dynamical
evolution of an open quantum system can be fully experimentally characterized.
We demonstrate explicitly how this procedure can be implemented with a nuclear
magnetic resonance quantum computer. This allows us to measure the fidelity of
a controlled-not logic gate and to experimentally investigate the error model
for our computer. Based on the latter analysis, we test an important assumption
underlying nearly all models of quantum error correction, the independence of
errors on different qubits.Comment: 8 pages, 7 EPS figures, REVTe
A pilot ASKAP survey for radio transients towards the Galactic Centre
We present the results of a radio transient and polarisation survey towards
the Galactic Centre, conducted as part of the Australian Square Kilometre Array
Pathfinder Variables and Slow Transients pilot survey. The survey region
consisted of five fields covering (, ). Each field was observed
for 12\,minutes, with between 7 and 9 repeats on cadences of between one day
and four months. We detected eight highly variable sources and seven highly
circularly-polarised sources (14 unique sources in total). Seven of these
sources are known pulsars including the rotating radio transient
PSR~J1739--2521 and the eclipsing pulsar PSR~J1723--2837. One of them is a low
mass X-ray binary, 4U 1758--25. Three of them are coincident with optical or
infrared sources and are likely to be stars. The remaining three may be related
to the class of Galactic Centre Radio Transients (including a highly likely
one, VAST~J173608.2--321634, that has been reported previously), although this
class is not yet understood. In the coming years, we expect to detect 40
bursts from this kind of source with the proposed four-year VAST survey if the
distribution of the source is isotropic over the Galactic fields.Comment: 17 pages, 13 figures, Accepted for publication in MNRA
Recommended from our members
Simulated 50 % radiation dose reduction in coronary CT angiography using adaptive iterative dose reduction in three-dimensions (AIDR3D)
To compare the image quality of coronary CT angiography (CTA) studies between standard filtered back projection (FBP) and adaptive iterative dose reduction in three-dimensions (AIDR3D) reconstruction using CT noise additional software to simulate reduced radiation exposure. Images from 93 consecutive clinical coronary CTA studies were processed utilizing standard FBP, FBP with 50 % simulated dose reduction (FBP50 %), and AIDR3D with simulated 50 % dose reduction (AIDR50 %). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured within 5 regions-of-interest, and image quality for each reconstruction strategy was assessed by two independent readers using a 4-point scale. Compared to FBP, the SNR measured from the AIDR50 % images was similar or higher (airway: 38.3 ± 12.7 vs. 38.5 ± 14.5, p = 0.81, fat: 5.5 ± 1.9 vs. 5.4 ± 2.0, p = 0.20, muscle: 3.2 ± 1.2 vs. 3.1 ± 1.3, p = 0.38, aorta: 22.6 ± 9.4 vs. 20.2 ± 9.7, p < 0.0001, liver: 2.7 ± 1.0 vs. 2.3 ± 1.1, p < 0.0001), while the SNR of the FBP50 % images were all lower (p values < 0.0001). The CNR measured from AIDR50 % images was also higher than that from the FBP images for the aorta relative to muscle (20.5 ± 9.0 vs. 18.3 ± 9.2, p < 0.0001). The interobserver agreement in the image quality score was excellent (Îș = 0.82). The quality score was significantly higher for the AIDR50 % images compared to the FBP images (3.6 ± 0.6 vs. 3.3 ± 0.7, p = 0.004). Simulated radiation dose reduction applied to clinical coronary CTA images suggests that a 50 % reduction in radiation dose can be achieved with adaptive iterative dose reduction software with image quality that is at least comparable to images acquired at standard radiation exposure and reconstructed with filtered back projection
Lower bounds on the complexity of simulating quantum gates
We give a simple proof of a formula for the minimal time required to simulate
a two-qubit unitary operation using a fixed two-qubit Hamiltonian together with
fast local unitaries. We also note that a related lower bound holds for
arbitrary n-qubit gates.Comment: 6 page
Classical Novae in the ASKAP Pilot Surveys
We present a systematic search for radio counterparts of novae using the
Australian Square Kilometer Array Pathfinder (ASKAP). Our search used the Rapid
ASKAP Continuum Survey, which covered the entire sky south of declination
( square degrees) at a central frequency of 887.5
MHz, the Variables and Slow Transients Pilot Survey, which covered
square degrees per epoch (887.5 MHz), and other ASKAP pilot surveys, which
covered square degrees with 2-12 hour integration times. We
crossmatched radio sources found in these surveys over a two-year period, from
April 2019 to August 2021, with 440 previously identified optical novae, and
found radio counterparts for four novae: V5668 Sgr, V1369 Cen, YZ Ret, and RR
Tel. Follow-up observations with the Australian Telescope Compact Array confirm
the ejecta thinning across all observed bands with spectral analysis indicative
of synchrotron emission in V1369 Cen and YZ Ret. Our light-curve fit with the
Hubble Flow model yields a value of
for the mass ejected in V1369 Cen. We also derive a peak surface brightness
temperature of K for YZ Ret. Using Hubble Flow model simulated radio
lightcurves for novae, we demonstrate that with a 5 sensitivity limit
of 1.5 mJy in 15-min survey observations, we can detect radio emission up to a
distance of 4 kpc if ejecta mass is in the range , and
upto 1 kpc if ejecta mass is in the range . Our
study highlights ASKAP's ability to contribute to future radio observations for
novae within a distance of 1 kpc hosted on white dwarfs with masses
, and within a distance of 4 kpc hosted on white dwarfs
with masses .Comment: This paper has been accepted for publication in PASA. It consists of
13 pages, 5 figures and 4 table
- âŠ