Energetic Suppression of Decoherence in Exchange-Only Quantum Computation

Universal quantum computation requiring only the Heisenberg exchange interaction and suppressing decoherence via an energy gap is presented. The combination of an always-on exchange interaction between the three physical qubits comprising the encoded qubit and a global magnetic field generates an energy gap between the subspace of interest and all other states. This energy gap suppresses decoherence. Always-on exchange couplings greatly simplify hardware specifications and the implementation of inter-logical-qubit gates. A controlled phase gate can be implemented using only three Heisenberg exchange operations all of which can be performed simultaneously.Comment: 4 pages, 4 figure

Quantum Cellular Automata Pseudo-Random Maps

Quantum computation based on quantum cellular automata (QCA) can greatly reduce the control and precision necessary for experimental implementations of quantum information processing. A QCA system consists of a few species of qubits in which all qubits of a species evolve in parallel. We show that, in spite of its inherent constraints, a QCA system can be used to study complex quantum dynamics. To this aim, we demonstrate scalable operations on a QCA system that fulfill statistical criteria of randomness and explore which criteria of randomness can be fulfilled by operators from various QCA architectures. Other means of realizing random operators with only a few independent operators are also discussed.Comment: 7 pages, 8 figures, submitted to PR

A Scalable Architecture for Coherence-Preserving Qubits

We propose scalable architectures for the coherence-preserving qubits introduced by Bacon, Brown, and Whaley [Phys. Rev. Lett. {\bf 87}, 247902 (2001)]. These architectures employ extra qubits providing additional degrees of freedom to the system. We show that these extra degrees of freedom can be used to counter errors in coupling strength within the coherence-preserving qubit and to combat interactions with environmental qubits. The presented architectures incorporate experimentally viable methods for inter-logical-qubit coupling and can implement a controlled phase gate via three simultaneous Heisenberg exchange operations. The extra qubits also provide flexibility in the arrangement of the physical qubits. Specifically, all physical qubits of a coherent-preserving qubit lattice can be placed in two spatial dimensions. Such an arrangement allows for universal cluster state computation.Comment: 4 pages, 4 figure

Large-amplitude electron-acoustic solitons in a dusty plasma with kappa-distributed electrons

The Sagdeev pseudopotential method is used to investigate the occurrence and the dynamics of fully nonlinear electrostatic solitary structures in a plasma containing suprathermal hot electrons, in the presence of massive charged dust particles in the background. The soliton existence domain is delineated, and its parametric dependence on different physical parameters is clarified.Comment: 3 pages, 1 figure, presented as a poster at the 6th International Conference on the Physics of Dusty Plasmas (ICPDP6), Garmisch-Partenkirchen, Germany, 201

Hole-pair hopping in arrangements of hole-rich/hole-poor domains in a quantum antiferromagnet

We study the motion of holes in a doped quantum antiferromagnet in the presence of arrangements of hole-rich and hole-poor domains such as the stripe-phase in high-$T_C$ cuprates. When these structures form, it becomes energetically favorable for single holes, pairs of holes or small bound-hole clusters to hop from one hole-rich domain to another due to quantum fluctuations. However, we find that at temperature of approximately 100 K, the probability for bound hole-pair exchange between neighboring hole-rich regions in the stripe phase, is one or two orders of magnitude larger than single-hole or multi-hole droplet exchange. As a result holes in a given hole-rich domain penetrate further into the antiferromagnetically aligned domains when they do it in pairs. At temperature of about 100 K and below bound pairs of holes hop from one hole-rich domain to another with high probability. Therefore our main finding is that the presence of the antiferromagnetic hole-poor domains act as a filter which selects, from the hole-rich domains (where holes form a self-bound liquid), hole pairs which can be exchanged throughout the system. This fluid of bound hole pairs can undergo a superfluid phase ordering at the above mentioned temperature scale.Comment: Revtex, 6 two-column pages, 4 figure

Effects of Poor Sanitation Procedures on Cross-Contamination of Animal Species in Ground Meat Products

The presence of \u3c1% of an undeclared species in ground meat is generally thought to be indicative of cross-contamination as opposed to intentional mislabeling; however, this has not been experimentally tested. The objective of this study was to quantify the effects of poor sanitation on the cross-contamination of animal species in ground meat products, with the example of undeclared pork in ground beef. Cross-contamination was quantified using real-time polymerase chain reaction (PCR). Three different sanitation treatments were tested with a commercial grinder (“no cleaning”, “partial cleaning”, or “complete cleaning”) in between grinding of pork and beef samples (13.6 kg each). A 100-g sample was collected for each 0.91 kg (2 lb) of beef processed with the grinder and each sanitation treatment was tested twice. For the “no cleaning” treatment, the first 100-g sample of ground beef run through the grinder contained 24.42 ± 10.41% pork, while subsequent samples (n = 14) contained \u3c0.2% pork. With “partial cleaning,” the first sample of ground beef contained 4.60 ± 0.3% pork and subsequent samples contained \u3c0.2% pork. Pork was not detected in ground beef following “complete cleaning.” These results indicate that incomplete cleaning of grinding equipment leads to species cross-contamination at levels of \u3c1% in most cases. Proper sanitation procedures must be followed when grinding multiple species in order to prevent cross-contamination and product mislabeling

Identification of Species in Ground Meat Products Sold on the U.S. Commercial Market Using DNA-Based Methods

The objective of this study was to test a variety of ground meat products sold on the U.S. commercial market for the presence of potential mislabeling. Forty-eight ground meat samples were purchased from online and retail sources, including both supermarkets and specialty meat retailers. DNA was extracted from each sample in duplicate and tested using DNA barcoding of the cytochrome c oxidase I (COI) gene. The resulting sequences were identified at the species level using the Barcode of Life Database (BOLD). Any samples that failed DNA barcoding went through repeat extraction and sequencing, and due to the possibility of a species mixture, they were tested with real-time polymerase chain reaction (PCR) targeting beef, chicken, lamb, turkey, pork and horse. Of the 48 samples analyzed in this study, 38 were labeled correctly and 10 were found to be mislabeled. Nine of the mislabeled samples were found to contain additional meat species based on real-time PCR, and one sample was mislabeled in its entirety. Interestingly, meat samples ordered from online specialty meat distributors had a higher rate of being mislabeled (35%) compared to samples purchased from a local butcher (18%) and samples purchased at local supermarkets (5.8%). Horsemeat, which is illegal to sell on the U.S. commercial market, was detected in two of the samples acquired from online specialty meat distributors. Overall, the mislabeling detected in this study appears to be due to either intentional mixing of lower-cost meat species into higher cost products or unintentional mixing of meat species due to cross-contamination during processing

Quantum Fidelity Decay of Quasi-Integrable Systems

We show, via numerical simulations, that the fidelity decay behavior of quasi-integrable systems is strongly dependent on the location of the initial coherent state with respect to the underlying classical phase space. In parallel to classical fidelity, the quantum fidelity generally exhibits Gaussian decay when the perturbation affects the frequency of periodic phase space orbits and power-law decay when the perturbation changes the shape of the orbits. For both behaviors the decay rate also depends on initial state location. The spectrum of the initial states in the eigenbasis of the system reflects the different fidelity decay behaviors. In addition, states with initial Gaussian decay exhibit a stage of exponential decay for strong perturbations. This elicits a surprising phenomenon: a strong perturbation can induce a higher fidelity than a weak perturbation of the same type.Comment: 11 pages, 11 figures, to be published Phys. Rev.