Triplet Superconductors from the Viewpoint of Basic Elements for Quantum Computers

We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing.Comment: 4 pages, 5 figures, will be presented at ASC-2002 and submitted to IEEE Trans. Appl. Supercon

X ray timing observations and gravitational physics

Photon-rich x ray observations on bright compact galactic sources will make it possible to detect many fast processes that may occur in these systems on millisecond and submillisecond timescales. Many of these processes are of direct relevance to gravitational physics because they arise in regions of strong gravity near neutron stars and black holes where the dynamical timescales for compact objects of stellar mass are milliseconds. To date, such observations have been limited by the detector area and telemetry rates available. However, instruments such as the proposed X ray Large Array (XLA) would achieve collecting areas of about 100 sq m. This instrument has been described elsewhere (Wood and Michelson 1988) and was the subject of a recent prephase A feasibility study at Marshall Space Flight Center. Observations with an XLA class instrument will directly impact five primary areas of astrophysics research: the attempt to detect gravitational radiation, the study of black holes, the physics of mass accretion onto compact objects, the structure of neutron stars and nuclear matter, and the characterization of dark matter in the universe. Those observations are discussed that are most directly relevant to gravitational physics: the search for millisecond x ray pulsars that are potential sources of continuous gravitational radiation; and the use of x ray timing observations to probe the physical conditions in extreme relativistic regions of space near black holes, both stellar-sized and supermassive

X-Ray Eclipse Timing in the LMXB EXO0748-676

Orbital period changes are an important diagnostic for understanding low mass X-ray binary (LMXB) accretion-induced angular momentum exchange and overall system evolution. We present our most recent results for the eclipse timing of the LMXB EXO0748-676. Since its discovery in 1985 it has apparently undergone three distinct orbital period "epochs", each characterized by a different orbital period than the previous epoch. We outline the orbital period behavior for EXO0748-676 over the past 18 years and discuss the implications of this behavior in light of current theoretical ideas for LMXB evolution.Comment: 4 Pages, 3 Figures, Submitted to the X-Ray Timing 2003: Rossi and Beyond conference, November 200

Possible Magnetic Activity in the Low Mass X-ray Binary EXO 0748-676

We report evidence of magnetic activity associated with the secondary star in the EXO 0748-676 low mass X-ray binary system. An analysis of a sequence of five consecutive X-ray eclipses observed during December 2003 with the RXTE satellite brings out a feature occurring during ingress we interpret as the X-ray photoelectric absorption shadow, as seen by an observer at Earth, of a plasma structure suspended above the surface of the secondary star. The light curve feature consists of an initial drop in count rate to near zero (the absorption shadow) with a very short rebound to a significant fraction of the pre-ingress count rate and then a final plunge to totality over a total time scale of ~25 s. The ingress feature persists for at least 5 consecutive orbital periods (a total of ~19 hr), and possibly up to 5 days in our data. Our data also show significant post-egress dipping during this eclipse sequence, unusual for this source, indicating possible secondary star mass ejection during this episode.Comment: Accepted by Astrophysical Journal Letters; 11 Pages including 3 figures and 1 tabl

A Strong X-Ray Burst from the Low Mass X-Ray Binary EXO0748-676

We have observed an unusually strong X-ray burst as a part of our regular eclipse timing observations of the low mass binary system EXO0748-676. The burst peak flux was 5.2x10^-8 ergs cm^-2 s^-1, approximately five times the normal peak X-ray burst flux observed from this source by RXTE. Spectral fits to the data strongly suggest that photospheric radius expansion occurred during the burst. In this Letter we examine the properties of this X-ray burst, which is the first example of a radius expansion burst from EXO0748-676 observed by RXTE. We find no evidence for coherent burst oscillations. Assuming that the peak burst luminosity is the Eddington luminosity for a 1.4 solar mass neutron star we derive a distance to EXO0748-676 of 7.7 kpc for a helium-dominated burst photosphere and 5.9 kpc for a hydrogen-dominated burst photosphere.Comment: 15 pages including 2 figures and 1 table. Accepted for publication in the Astrophysical Journa

Triplet Superconductors from the Viewpoint of Basic Elements for Quantum Computers

We discuss possibilities of utilizing superconductors with Cooper condensates in triplet pairing states (where the spin of condensate pairs is S=1) for practical realization of quantum computers. Superconductors with triplet pairing condensates have features that are unique and cannot be found in the usual (singlet pairing, S=0) superconductors. The symmetry of the order parameter in some triplet superconductors (e.g., ruthenates) corresponds to doubly-degenerate chiral states. These states can serve as qubit base states for quantum computing