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D Bacon

Publications and source records attributed to D Bacon.

18 recordsLinked to original sources
PubMed2003

Bell inequalities with auxiliary communication.

What is the communication cost of simulating the correlations produced by quantum theory? We generalize Bell inequalities to the setting of local realistic theories augmented by a fixed amount of classical communication. Suppose two parties choose one of M two-outcome measurements and exchange 1 bit of information. We present the complete set of inequalities for M=2, and the complete set of inequalities for the joint correlation observable for M=3. We find that correlations produced by quantum theory satisfy both of these sets of inequalities. One bit of communication is therefore sufficient to simulate quantum correlations in both of these scenarios.

Journal Article↗
PubMed2001

Coherence-preserving quantum bits.

Real quantum systems couple to their environment and lose their intrinsic quantum nature through the process known as decoherence. Here we present a method for minimizing decoherence by making it energetically unfavorable. We present a Hamiltonian made up solely of two-body interactions between four two-level systems (qubits) which has a 2-fold degenerate ground state. This degenerate ground state has the property that any decoherence process acting on an individual physical qubit must supply energy from the bath to the system. Quantum information can be encoded into the degeneracy of the ground state and such coherence-preserving qubits will then be robust to local decoherence at low bath temperatures. We show how this quantum information can be universally manipulated and indicate how this approach may be applied to a quantum dot quantum computer.

Journal Article↗
PubMed2000

Universal quantum computation with the exchange interaction.

Various physical implementations of quantum computers are being investigated, although the requirements that must be met to make such devices a reality in the laboratory at present involve capabilities well beyond the state of the art. Recent solid-state approaches have used quantum dots, donor-atom nuclear spins or electron spins; in these architectures, the basic two-qubit quantum gate is generated by a tunable exchange interaction between spins (a Heisenberg interaction), whereas the one-qubit gates require control over a local magnetic field. Compared to the Heisenberg operation, the one-qubit operations are significantly slower, requiring substantially greater materials and device complexity--potentially contributing to a detrimental increase in the decoherence rate. Here we introduced an explicit scheme in which the Heisenberg interaction alone suffices to implement exactly any quantum computer circuit. This capability comes at a price of a factor of three in additional qubits, and about a factor of ten in additional two-qubit operations. Even at this cost, the ability to eliminate the complexity of one-qubit operations should accelerate progress towards solid-state implementations of quantum computation.

Journal Article↗
PubMed2000

Long-term outcome of surgery for dogs with cranial cruciate ligament deficiency.

Fifty-eight dogs with cranial cruciate ligament deficiency were assessed and treated surgically. At an average of 50 months postoperatively, the functional outcome was assessed by means of an owner-based clinical assessment and a clinical examination. Client-based data were available for 26 dogs and 20 dogs were reassessed after 50 months. The results were compared with the initial values and with data from an assessment 13 months postoperatively. The level of disability at 50 months was judged to be significantly less than initially. However, there were no differences between the initial assessments and those made after 50 months for the perceived 'effect of cold weather' and the dogs' 'ability to jump', despite both measures having improved after 13 months. Age and meniscal injury were identified as poor prognostic indicators for the long-term outcome. The equivalent joint on the contralateral limb deteriorated significantly during the study.

Animals↗
PubMed2000

Universal fault-tolerant quantum computation on decoherence-free subspaces

A general scheme to perform universal, fault-tolerant quantum computation within decoherence-free subspaces (DFSs) is presented. At most two-qubit interactions are required, and the system remains within the DFS throughout the entire implementation of a quantum gate. We show explicitly how to perform universal computation on clusters of the four-qubit DFS encoding one logical qubit each under spatially symmetric (collective) decoherence. Our results have immediate relevance to quantum computer implementations in which quantum logic is implemented through exchange interactions, such as the recently proposed spin-spin coupled quantum dot arrays and donor-atom arrays.

Journal Article↗
PubMed1997

Asystole as a neurologic sign.

The authors present a case of asystole occurring during dural closure following craniotomy with the patient in the supine position. This 22-year-old woman had a left parietal lobe tumor resected with bipolar cautery. Standard intraoperative monitoring with a left radial arterial line and a right internal jugular central venous catheter was used during the surgery. The anesthetic course was complicated by intraoperative bleeding that responded to three units of fresh frozen plasma. Prior to closure, the operative site appeared dry and intact. After closure, asystole occurred suddenly and resolved with evacuation of 500 ml of blood. It is speculated that the asystole was preceded by an acute increase in intracranial pressure and a subsequent secondary brainstem compression.

Adult↗
PubMed1994

Comparison of systematic search and database methods for constructing segments of protein structure.

Two principal methods of determining the conformation of short pieces of polypeptide backbone in proteins have been developed: using a database of known structures and systematically generating all conformations. In this paper, we compare the effectiveness of these two techniques. The completeness of the database for segments of different lengths is examined and it is found to contain most conformations for segments seven residues long, but to deteriorate rapidly for longer regions. When the database segment is to be incorporated into the rest of a structure, at least seven residues are required to build four new residues, because of the need to position the segment relative to the rest of the structure. It is found that such positioning using flanking residues results in large errors in the inserted region. We conclude that the database method is currently not effective for comparative modeling, even for short segments. The systematic search procedure is found to generate almost all structures of short segments found in proteins. In contrast to the database method, low root mean square error structures are obtained for a set of trial segments embedded in the rest of a protein structure. Thus, it should be considered the method of choice.

Computer Simulation↗
PubMed1985

Pheochromocytoma with hypercalcemia: case report and review of literature.

We report a case of severe hypercalcemia and a pheochromocytoma of the right adrenal gland. The patient underwent adrenalectomy, following which the hypercalcemia disappeared. Parathormone assay of the adrenal tumor revealed high levels of activity despite normal serum parathormone activity. This suggests that the etiology of hypercalcemia in patients with pheochromocytoma is related to ectopic secretion of a parathormone ectopic peptide-like substance.

Adrenal Gland Neoplasms↗