Non-Metaphysical Realism: A Dummett-Inspired Implementation of Putnam’s Internal Realism

The amount of realist positions put forward by philosophers of religion and theologians is impressive. one can certainly doubt whether there is a need for yet another alternative. However, most realist positions employed in studies on religion fall prey to Hilary Putnam’s criticism against metaphysical realism. This gives rise to a dilemma that I aim at solving by introducing yet another realist position, namely non-metaphysical realism

On the error probability of general tree and trellis codes with applications to sequential decoding

An upper bound on the average error probability for maximum-likelihood decoding of the ensemble of random binary tree codes is derived and shown to be independent of the length of the tree. An upper bound on the average error probability for maximum-likelihood decoding of the ensemble of random L-branch binary trellis codes of rate R = 1/n is derived which separates the effects of the tail length T and the memory length M of the code. It is shown that the bound is independent of the length L of the information sequence. This implication is investigated by computer simulations of sequential decoding utilizing the stack algorithm. These simulations confirm the implication and further suggest an empirical formula for the true undetected decoding error probability with sequential decoding

Decoherence from spin environments: Loschmidt echo and quasiparticle excitations

We revisit the problem of decoherence of a qubit centrally coupled to an interacting spin environment, here modeled by a quantum compass chain or an extended XY model in a staggered magnetic field. These two models both support distinct spin liquid phases, adding a new element to the problem. By analyzing their Loschmidt echoes when perturbed by the qubit we find that a fast decoherence of the qubit is conditioned on the presence of propagating quasiparticles which couple to it. Different from expectations based on earlier works on central spin models, our result implies that the closeness of an environment to a quantum phase transition is neither a sufficient nor a necessary condition for an accelerated decoherence rate of a qubit.Comment: 13 pages, 9 figure

The two-impurity Kondo model with spin-orbit interactions

We study the two-impurity Kondo model (TIKM) in two dimensions with spin-orbit coupled conduction electrons. In the first part of the paper we analyze how spin-orbit interactions of Rashba as well as Dresselhaus type influence the Kondo and RKKY interactions in the TIKM, generalizing results obtained by H. Imamura {\em et al.} (2004) and J. Malecki (2007). Using our findings we then explore the effect from spin-orbit interactions on the non-Fermi liquid quantum critical transition between the RKKY-singlet and Kondo-screened RKKY-triplet states. We argue that spin-orbit interactions under certain conditions produce a line of critical points exhibiting the same leading scaling behavior as that of the ordinary TIKM. In the second part of the paper we shift focus and turn to the question of how spin-orbit interactions affect the entanglement between two localized RKKY-coupled spins in the parameter regime where the competition from the direct Kondo interaction can be neglected. Using data for a device with two spinful quantum dots patterned in a gated InAs heterostructure we show that a gate-controlled spin-orbit interaction may drive a maximally entangled state to one with vanishing entanglement, or vice versa (as measured by the concurrence). This has important implications for proposals using RKKY interactions for nonlocal control of qubit entanglement in semiconductor heterostructures.Comment: Revised version; new title and introduction in response to referee suggestion, expanded discussion of results, added references. 14 pages, 5 figure

Anticipated verbal feedback induces altruistic behavior

A distinctive feature of humans compared to other species is the high rate of cooperation with non-kin. One explanation is that humans are motivated by concerns for social esteem. In this paper we experimentally investigate the impact of anticipated verbal feedback on altruistic behavior. We study pairwise interactions in which one subject, the “divider”, decides how to split a sum of money between herself and a recipient. Thereafter, the recipient can send an unrestricted anonymous message to the divider. The subjects’ relationship is anonymous and one-shot to rule out any reputation effects. Compared to a control treatment without feedback messages, donations increase substantially when recipients can communicate. With verbal feedback, the fraction of zero donations decreases from about 40% to about 20%, and there is a corresponding increase in the fraction of equal splits from about 30% to about 50%. Recipients who receive no money almost always express disapproval of the divider, sometimes strongly and in foul language. Following an equal split, almost all recipients praise the divider. The results suggest that anticipated verbal rewards and punishments play a role in promoting altruistic behavior among humans.Punishment; Approval; Disapproval; Dictator game; Altruism; Communication; Verbal feedback

Generosity

We develop a simple model of generous behavior. It is based on the premise that some people are generous, but everyone wants to appear generous. Although non-monetary donations are always inefficient, our model predicts donors to favor non-monetary donations when the inefficiency is relatively small and when the recipient is sufficiently rich. The model helps to explain the prevalence of volunteering, the nature of Christmas gifts, and the taboo against paying cash in return for friendly favors. The model also explains why it is socially more acceptable to ask for favors than for money.Altruism; Non-monetary gifts; Volunteering

Controllable spin entanglement production in a quantum spin Hall ring

We study the entanglement production in a quantum spin Hall ring geometry where electrons of opposite spins are emitted in pairs from a source and collected in two different detectors. Postselection of coincidence detector events gives rise to entanglement in the system, measurable through correlations between the outcomes in the detectors. We have chosen a geometry such that the entanglement depends on the dynamical phases picked up by the edge states as they move around the ring. In turn, the dependence of the phases on gate potential and Rashba interaction allows for a precise electrical control of the entanglement production in the ring.Comment: 11 pages, 6 figures. Published version, new Fig. 3, added referenc