A discrete version of the WKB method is developed and applied to calculate the tunnel splittings between classically degenerate states of spin Hamiltonians. The results for particular model problems are in complete accord with those previously found using instanton methods. The discrete WKB method is more elementary and also yields wavefunctions. 03.65.Sq, 33.20.-t, 75.45.+j Typeset using REVTEX

Solid-state spin systems such as nitrogen-vacancy colour centres in diamond are promising for applications of quantum information, sensing and metrology. However, a key challenge for such solid-state systems is to realize a spin coherence time that is much longer than the time for quantum spin manipulation protocols. Here we demonstrate an improvement of more than two orders of magnitude in the...

Whatever dark matter is, it must be one irreducible unitary representation of the extended Lorentz group or another. We here develop a formalism mass dimension fermions and bosons spin half, show that they provide natural candidates. By construction, are covariant under space-time translations boosts. However, incorporating rotational symmetry is non-trivial requires introducing two-fold Wigner...

We show how to detect entanglement with criteria built from simple two-body correlation terms. Since many natural Hamiltonians are sums of such correlation terms, our ideas can be used to detect entanglement by energy measurement. Our criteria can straightforwardly be applied for detecting different forms of multipartite entanglement in familiar spin models in thermal equilibrium.

In this work, we have extended the factorization method of scalar shape-invariant Schrödinger Hamiltonians to a class Dirac-like matrix Hamiltonians. The intertwining operators equations been implemented in shape invariant equations. We considered also another kind anti-intertwining changing sign energy. can be obtained from reduction higher dimensional spin systems. Two examples worked out, on...

Inspired by Kitaev’s argument that physical error correction is possible in a system of interacting anyons, we demonstrate that such ”self-correction” is fairly common in spin systems with classical Hamiltonians that admit the Peierls argument and where errors are modelled by quantum perturbations.