794 research outputs found
Effective Hamiltonians for interacting superconducting qubits -- local basis reduction and the Schrieffer-Wolff transformation
An open question in designing superconducting quantum circuits is how best to
reduce the full circuit Hamiltonian which describes their dynamics to an
effective two-level qubit Hamiltonian which is appropriate for manipulation of
quantum information. Despite advances in numerical methods to simulate the
spectral properties of multi-element superconducting circuits, the literature
lacks a consistent and effective method of determining the effective qubit
Hamiltonian. Here we address this problem by introducing a novel local basis
reduction method. This method does not require any ad hoc assumption on the
structure of the Hamiltonian such as its linear response to applied fields. We
numerically benchmark the local basis reduction method against other
Hamiltonian reduction methods in the literature and report specific examples of
superconducting qubits, including the capacitively-shunted flux qubit, where
the standard reduction approaches fail. By combining the local basis reduction
method with the Schrieffer-Wolff transformation we further extend its
applicability to systems of interacting qubits and use it to extract both
non-stoquastic two-qubit Hamiltonians and three-local interaction terms in
three-qubit Hamiltonians
Rapid Thermal Annealing for Surface Optimisation of ZnO Substrates for MBE-Grown Oxide Two-Dimensional Electron Gases
Two-dimensional electron gases (2DEGs) at the ZnO/ZnMgO interface are
promising for applications in spintronics and quantum computing due to the
combination of low spin-orbit coupling and high electron mobility. Growing high
mobility 2DEGs requires high quality substrates with low impurity densities. In
this work we demonstrate a ZnO substrate sample treatment combining high
temperature rapid thermal annealing and chemical etching to improve the surface
quality for the subsequent growth of 2DEGs. This process enables the growth of
a 2DEG with low-temperature mobility of ~cmVs.
An unannealed control sample shows a scattering rate at least three times
greater than the annealed sample.Comment: 5 pages, 3 figure
Perturbed ferromagnetic chain: Tunable test of hardness in the transverse-field Ising model
Quantum annealing in the transverse-field Ising model (TFIM) with open-system dynamics is known to use thermally assisted tunneling to drive computation. However, it is still subject to debate whether quantum systems in the presence of decoherence are more useful than those using classical dynamics to drive computation. We contribute to this debate by introducing the perturbed ferromagnetic chain (PFC), a chain of frustrated subsystems where the degree of frustration scales inversely with the perturbation introduced by a tunable parameter. This gives us an easily embeddable gadget whereby problem hardness can be tuned for systems of constant size. We outline the properties of the PFC and compare classical spin-vector Monte Carlo (SVMC) variants with the adiabatic quantum master equation. We demonstrate that SVMC methods get trapped in the exponentially large first-excited-state manifold when solving this frustrated problem, whereas evolution using quantum dynamics remains in the lowest energy eigenstates. This results in significant differences in ground-state probability when using either classical or quantum annealing dynamics in the TFIM
Deliberate clinical inertia: Using meta-cognition to improve decision-making
Deliberate clinical inertia is the art of doing nothing as a positive response. To be able to apply this concept, individual clinicians need to specifically focus on their clinical decision-making. The skill of solving problems and making optimal clinical decisions requires more attention in medical training and should play a more prominent part of the medical curriculum. This paper provides suggestions on how this may be achieved. Strategies to mitigate common biases are outlined, with an emphasis on reversing a 'more is better' culture towards more temperate, critical thinking. To incorporate such an approach in medical curricula and in clinical practice, institutional endorsement and support is required
GHz bandwidth electro-optics of a single self-assembled quantum dot in a charge-tunable device
The response of a single InGaAs quantum dot, embedded in a miniaturized
charge-tunable device, to an applied GHz bandwidth electrical pulse is
investigated via its optical response. Quantum dot response times of 1.0 \pm
0.1 ns are characterized via several different measurement techniques,
demonstrating GHz bandwidth electrical control. Furthermore a novel optical
detection technique based on resonant electron-hole pair generation in the
hybridization region is used to map fully the voltage pulse experienced by the
quantum dot, showing in this case a simple exponential rise.Comment: 7 pages, 4 figure
Plasticity in Prefrontal Cortex Induced by Coordinated Synaptic Transmission Arising from Reuniens/Rhomboid Nuclei and Hippocampus
The nucleus reuniens and rhomboid nuclei of the thalamus (ReRh) are reciprocally connected to a range of higher order cortices including hippocampus (HPC) and medial prefrontal cortex (mPFC). The physiological function of ReRh is well predicted by requirement for interactions between mPFC and HPC, including associative recognition memory, spatial navigation, and working memory. Although anatomical and electrophysiological evidence suggests ReRh makes excitatory synapses in mPFC there is little data on the physiological properties of these projections, or whether ReRh and HPC target overlapping cell populations and, if so, how they interact. We demonstrate in ex vivo mPFC slices that ReRh and HPC afferent inputs converge onto more than two-thirds of layer 5 pyramidal neurons, show that ReRh, but not HPC, undergoes marked short-term plasticity during theta frequency transmission, and that HPC, but not ReRh, afferents are subject to neuromodulation by acetylcholine acting via muscarinic receptor M2. Finally, we demonstrate that pairing HPC followed by ReRh (but not pairing ReRh followed by HPC) at theta frequency induces associative, NMDA receptor dependent synaptic plasticity in both inputs to mPFC. These data provide vital physiological phenotypes of the synapses of this circuit and provide a novel mechanism for HPC–ReRh–mPFC encoding
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