Folly to the Greeks: Good Reasons to Give up Reason

A discussion of why a strong doctrine of 'reason' may not be worth sustaining in the face of modern scientific speculation, and the difficulties this poses for scientific rationality, together with comments on the social understanding of religion, and why we might wish to transcend common sense

Slavery, welfare and the sixth extinction

Ng’s laudable concern for animal welfare would be welcome to any sensible slave-owner wishing to preserve his investment. What welfarism – for slave-owners and animal husbandmen – fails to call into question is whether we have the right to breed, hold captive and kill animals at all: If it matters, as the widely recognized slogan of ‘Five Freedoms’ suggests, that animals have the chance to live a ‘normal’ life, then more matters than keeping them ‘happy’ in subjection. Their lives – and also the lives of wild things – also deserve respect

Dynamics, dephasing and clustering of impurity atoms in Bose-Einstein condensates

We investigate the influence of a Bose-Einstein condensate (BEC) on the properties of immersed impurity atoms, which are trapped in an optical lattice. Assuming a weak coupling of the impurity atoms to the BEC, we derive a quantum master equation for the lattice system. In the special case of fixed impurities with two internal states the atoms represent a quantum register and the quantum master equation reproduces the exact evolution of the qubits. We characterise the qubit dephasing which is caused by the interspecies coupling and show that the effect of sub- and superdecoherence is observable for realistic experimental parameters. Furthermore, the BEC phonons mediate an attractive interaction between the impurities, which has an important impact on their spatial distribution. If the lattice atoms are allowed to move, there occurs a sharp transition with the impurities aggregating in a macroscopic cluster at experimentally achievable temperatures. We also investigate the impact of the BEC on the transport properties of the impurity atoms and show that a crossover from coherent to diffusive behaviour occurs with increasing interaction strength.Comment: 22 pages, 8 figures, some typos correcte

Slavery, welfare and the sixth extinction

Ng’s laudable concern for animal welfare would be welcome to any sensible slave-owner wishing to preserve his investment. What welfarism – for slave-owners and animal husbandmen – fails to call into question is whether we have the right to breed, hold captive and kill animals at all: If it matters, as the widely recognized slogan of ‘Five Freedoms’ suggests, that animals have the chance to live a ‘normal’ life, then more matters than keeping them ‘happy’ in subjection. Their lives – and also the lives of wild things – also deserve respect

Unifying Neural-network Quantum States and Correlator Product States via Tensor Networks

Correlator product states (CPS) are a powerful and very broad class of states for quantum lattice systems whose (unnormalised) amplitudes in a fixed basis can be sampled exactly and efficiently. They work by gluing together states of overlapping clusters of sites on the lattice, called correlators. Recently Carleo and Troyer (2017 Science 355 602) introduced a new type sampleable ansatz called neural-network quantum states (NQS) that are inspired by the restricted Boltzmann model used in machine learning. By employing the formalism of tensor networks we show that NQS are a special form of CPS with novel properties. Diagramatically a number of simple observations become transparent. Namely, that NQS are CPS built from extensively sized GHZ-form correlators making them uniquely unbiased geometrically. The appearance of GHZ correlators also relates NQS to canonical polyadic decompositions of tensors. Another immediate implication of the NQS equivalence to CPS is that we are able to formulate exact NQS representations for a wide range of paradigmatic states, including superpositions of weighed-graph states, the Laughlin state, toric code states, and the resonating valence bond state. These examples reveal the potential of using higher dimensional hidden units and a second hidden layer in NQS. The major outlook of this study is the elevation of NQS to correlator operators allowing them to enhance conventional well-established variational Monte Carlo approaches for strongly correlated fermions.</p

Heat current rectification and mobility edges

We investigate how the presence of a single-particle mobility edge in a system can generate strong heat current rectification. Specifically, we study a quadratic bosonic chain subject to a quasi-periodic potential and coupled at its boundaries to spin baths of differing temperature. We find that rectification increases by orders of magnitude depending on the spatial position in the chain of localized eigenstates above the mobility edge. The largest enhancements occur when the coupling of one bath to the system is dominated by a localized eigenstate, while the other bath couples to numerous delocalized eigenstates. By tuning the parameters of the quasi-periodic potential it is thus possible to vary the amplitude, and even invert the direction, of the rectification.Comment: 5+3 pages 4+4 figure

Decoherence of a quantum memory coupled to a collective spin bath

We study the quantum dynamics of a single qubit coupled to a bath of interacting spins as a model for decoherence in solid state quantum memories. The spin bath is described by the Lipkin-Meshkov-Glick model and the bath spins are subjected to a transverse magnetic field. We investigate the qubit interacting via either an Ising- or an XY-type coupling term to subsets of bath spins of differing size. The large degree of symmetry of the bath allows us to find parameter regimes where the initial qubit state is revived at well defined times after the qubit preparation. These times may become independent of the bath size for large baths and thus enable faithful qubit storage even in the presence of strong coupling to a bath. We analyze a large range of parameters and identify those which are best suited for quantum memories. In general we find that a small number of links between qubit and bath spins leads to less decoherence and that systems with Ising coupling between qubit and bath spins are preferable.Comment: 13 pages, 8 figure

Does International Trump Domestic Trade? The Seed Potato Market in Canada

trade, potato, Agricultural and Food Policy, International Development,

Does International Trump Domestic Trade? The Seed Potato Market in Canada

trade, potato, Canada, Agricultural and Food Policy, International Development, International Relations/Trade,

Density Matrix Renormalization Group in the Heisenberg Picture

In some cases the state of a quantum system with a large number of subsystems can be approximated efficiently by the density matrix renormalization group, which makes use of redundancies in the description of the state. Here we show that the achievable efficiency can be much better when performing density matrix renormalization group calculations in the Heisenberg picture, as only the observable of interest but not the entire state is considered. In some non-trivial cases, this approach can even be exact for finite bond dimensions.Comment: version to appear in PRL, acronyms in title and abstract expanded, new improved numerical example