Two qubits can be entangled in two distinct temperature regions

We have found that for a wide range of two-qubit Hamiltonians the canonical-ensemble thermal state is entangled in two distinct temperature regions. In most cases the ground state is entangled; however we have also found an example where the ground state is separable and there are still two regions. This demonstrates that the qualitative behavior of entanglement with temperature can be much more complicated than might otherwise have been expected; it is not simply determined by the entanglement of the ground state, even for the simple case of two qubits. Furthermore, we prove a finite bound on the number of possible entangled regions for two qubits, thus showing that arbitrarily many transitions from entanglement to separability are not possible. We also provide an elementary proof that the spectrum of the thermal state at a lower temperature majorizes that at a higher temperature, for any Hamiltonian, and use this result to show that only one entangled region is possible for the special case of Hamiltonians without magnetic fields.Comment: 6 pages, 4 figures, many new result

Quantum Computation as Geometry

Quantum computers hold great promise, but it remains a challenge to find efficient quantum circuits that solve interesting computational problems. We show that finding optimal quantum circuits is essentially equivalent to finding the shortest path between two points in a certain curved geometry. By recasting the problem of finding quantum circuits as a geometric problem, we open up the possibility of using the mathematical techniques of Riemannian geometry to suggest new quantum algorithms, or to prove limitations on the power of quantum computers.Comment: 13 Pages, 1 Figur

Mobilization of the platinum group elements by low-temperature fluids: Implications for mineralization and the iridium controversy

Geochemical investigations on the widely dispersed Late Proterozoic Acraman impact ejecta horizon and its host marine shales in the Adelaide Geosyncline provide strong evidence for low-temperature mobilization of the platinum group elements (PGE), including Ir. The ejecta horizon was formed when the middle Proterozoic dacitic volcanics in the Gawler Ranges, central South Australia, were impacted by a very large (ca. 4 km) meteorite. The resulting structure, now represented by Lake Acraman, is Australia's largest meteorite impact structure. Debris from the impact was blasted for many hundreds of kilometers, some falling into the shallow sea of the Adelaide Geosyncline, some 300 km to the east of the impact site

A proposed governance model for the adoption of geoparks in Australia

Purpose Good governance is crucial in establishing and managing geoparks and is a requirement by UNESCO if global status is to be achieved. Australia has three levels of government, government agencies and not for profit organisations that can assist in the reintroduction of geoparks to Australia. This paper examines a range of governance models used by UNESCO Global Geoparks. Design/methodology/approach This paper explores mechanisms that could be applied in the reintroduction of geoparks into Australia and considers how future geoparks might be managed. The suggested model is based on a review of existing UNESCO Global Geopark governance and their management structures. Findings This paper reviews the opportunities for engaging with Australian organisational stakeholders to support geoparks and proposes a model that would be suitable for adoption in Australia. Originality/value This paper examines a range of governance models applied to geopark development. It reviews the opportunities for engaging with Australian organisational stakeholders to support geoparks and proposes a model that would be suitable for adoption in Australia. Such an account has not previously been undertaken nor a satisfactory model proposed for the Australian situation. This is the first time that a comprehensive model for geopark governance has been proposed for Australia

Geoparks – learnings from Australia

Purpose This study aims to provide an overview of the current socio-political geopark situation in Australia and set this into a global context. In addition, the authors consider this information to be useful for all stakeholders involved in geopark research and development. An analysis of constraints is set alongside stakeholder views collected from remote rural Western Australia. The authors also place Australia in a global context in regard to the future of geoparks. Design/methodology/approach Vital contextual information regarding the tourism significance of geoparks is sourced from key literature. The authors analyse and report on the situation surrounding the current lack of enthusiasm for the geopark concept by the federal government and states in Australia. The authors also report positive rural community stakeholder views on geopark development from regional Western Australia. Findings While Australian federal, as well as state governments have yet to accept geoparks, stakeholder research in Western Australia supports the idea of geopark development. Learnings articulated in this viewpoint are relevant to any country pursuing and initiating the geopark concept. The authors posit that global geopark development can become a vital strategy in post-COVID-19 tourism recovery planning. Originality/value Australia currently does not have a United Nations Educational, Scientific and Cultural Organisation (UNESCO)-recognised geopark. Accordingly, the authors present a case for geopark development, while at the same time exploring the socio-political reasons behind the lack of geopark implementation in Australia. The authors consider the future of geoparks in the global context and reiterate the point that geoparks are important for COVID-19 recovery of tourism and in regard to UNESCO's Sustainable Development Goals for 2030

The Vortex Phase Qubit: Generating Arbitrary, Counter-Rotating, Coherent Superpositions in Bose-Einstein Condensates via Optical Angular Momentum Beams

We propose a scheme for generation of arbitrary coherent superposition of vortex states in Bose-Einstein condensates (BEC) using the orbital angular momentum (OAM) states of light. We devise a scheme to generate coherent superpositions of two counter-rotating OAM states of light using known experimental techniques. We show that a specially designed Raman scheme allows transfer of the optical vortex superposition state onto an initially non-rotating BEC. This creates an arbitrary and coherent superposition of a vortex and anti-vortex pair in the BEC. The ideas presented here could be extended to generate entangled vortex states, design memories for the OAM states of light, and perform other quantum information tasks. Applications to inertial sensing are also discussed.Comment: 4 pages, 4 figures, Revtex4, to be submitted to Phys. Rev. Let

Effect of an atom on a quantum guided field in a weakly driven fiber-Bragg-grating cavity

We study the interaction of an atom with a quantum guided field in a weakly driven fiber-Bragg-grating (FBG) cavity. We present an effective Hamiltonian and derive the density-matrix equations for the combined atom-cavity system. We calculate the mean photon number, the second-order photon correlation function, and the atomic excited-state population. We show that, due to the confinement of the guided cavity field in the fiber cross-section plane and in the space between the FBG mirrors, the presence of the atom in the FBG cavity can significantly affect the mean photon number and the photon statistics even though the cavity finesse is moderate, the cavity is long, and the probe field is weak.Comment: Accepted for Phys. Rev.