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We illustrate that open quantum systems composed of neutral, ultracold atoms in one-dimensional optical lattices can exhibit behavior analogous to semiconductor electronic circuits. A correspondence is demonstrated for bosonic atoms, and the experimental requirements to realize these devices are established. The analysis follows from a derivation of a quantum master equation for this general class of open quantum systems.
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Unipolar devices constructed from ferromagnetic semiconducting materials with variable magnetization direction are shown theoretically to behave very similarly to nonmagnetic bipolar devices such as the p-n diode and the bipolar (junction) transistor. Such devices may be applicable for magnetic sensing, nonvolatile memory, and reprogrammable logic.
We study in this article how heat can be exchanged between two level systems (TLS) each of them being coupled to a thermal reservoir. Calculation are performed solving a master equation for the density matrix using the Born markov-approximation. We analyse the conditions for which a thermal diode and a thermal transistor can be obtained as well as their optimization.
Transistors play a vital role in classical computers, and their quantum mechanical counterparts could potentially be as important in quantum computers. Where a classical transistor is operated as a switch that either blocks or allows an electric current, the quantum transistor should operate on quantum information. In terms of a spin model the in-going quantum information is an arbitrary qubit state (spin-1/2 state). In this paper, we derive a model of four qubits with Heisenberg interactions that works as a quantum spin transistor, i.e. a system with perfect state transfer or perfect blockade depending on the state of two gate qubits. When the system is initialized the dynamics complete the gate operation, hence our protocol requires minimal external control. We propose a concrete implementation of the model using state-of-the-art superconducting circuits. Finally, we demonstrate that our proposal operates with high-fidelity under realistic decoherence.
Vertical $pn$ heterojunction diodes were prepared by plasma-assisted molecular beam epitaxy of unintentionally-doped $p$-type SnO layers with hole concentrations ranging from $p=10^{18}$ to $10^{19}$cm$^{-3}$ on unintentionally-doped $n$-type $beta$-Ga$_{2}$O$_{3}$(-201) substrates with an electron concentration of $n=2.0times10^{17}$cm$^{-3}$. The SnO layers consist of (001)-oriented grains without in-plane expitaxial relation to the substrate. After subsequent contact processing and mesa etching (which drastically reduced the reverse current spreading in the SnO layer and associated high leakage) electrical characterization by current-voltage and capacitance-voltage measurement was performed. The results reveal a type-I band alignment and junction transport by thermionic emission in forward bias. A rectification of $2times10^{8}$ at $pm1$V, an ideality factor of 1.16, differential specific on-resistance of 3.9m$Omegathinspace$cm$^{2}$, and built-in voltage of 0.96V were determined. The $pn$-junction isolation prevented parallel conduction in the highly-conductive Ga$_{2}$O$_{3}$ substrate (sheet resistance $R_{S}approx3thinspaceOmega$) during van-der-Pauw Hall measurements of the SnO layer on top ($R_{S}approx150$k$Omega$, $papprox2.5times10^{18}$cm$^{-3}$, Hall mobility $approx1$cm$^{2}$/Vs). The measured maximum reverse breakdown voltage of the diodes was 66V, corresponding to a peak breakdown field 2.2MV/cm in the Ga$_{2}$O$_{3}$-depletion region. Higher breakdown voltages that are required in high-voltage devices could be achieved by reducing the donor concentration in the $beta$-Ga$_{2}$O$_{3}$ to increase the depletion width as well as improving the contact geometry to reduce field crowding.
Alternating current (ac) circuits can have electromagnetic edge modes protected by symmetries, analogous to topological band insulators or semimetals. How to make such a topological circuit? This paper illustrates a particular design idea by analyzing a series of topological circuits consisting purely of inductors (L) and capacitors (C) connected to each other by wires to form periodic lattices. All the examples are treated using a unifying approach based on Lagrangians and the dynamical $H$-matrix. First, the building blocks and permutation wiring are introduced using simple circuits in one dimension, the SSH transmission line and a braided ladder analogous to the ice-tray model also known as the $pi$-flux ladder. Then, more general building blocks (loops and stars) and wiring schemes ($m$-shifts) are introduced. The key concepts of emergent pseudo-spin degrees of freedom and synthetic gauge fields are discussed, and the connection to quantum lattice Hamiltonians is clarified. A diagrammatic notation is introduced to simplify the design and presentation of more complicated circuits. These building blocks are then used to construct topological circuits in higher dimensions. The examples include the circuit analog of Haldanes Chern insulator in two dimensions and quantum Hall insulator in four dimensions featuring finite second Chern numbers. The topological invariants and symmetry protection of the edge modes are discussed based on the $H$-matrix.
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