Quantum Switch Research Articles

Switchable Quantum Anomalous Hall State in a Strongly Frustrated Lattice Magnet

We establish that the interplay of itinerant fermions with localized magnetic moments on a checkerboard lattice leads to magnetic flux phases. For weak itineracy the flux phase is coplanar and the electronic dispersion takes the shape of graphenelike Dirac fermions. Stronger itineracy drives the formation of a noncoplanar, chiral flux phase, in which the Dirac fermions acquire a topological mass that is proportional to a ferromagnetic spin polarization. Consequently the system self-organizes into a ferromagnetic quantum anomalous Hall state in which the direction of its dissipationless edge currents can be switched by an applied magnetic field.

Quantum Switching of π-Electron Rotations in a Nonplanar Chiral Molecule by Using Linearly Polarized UV Laser Pulses

Nonplanar chiral aromatic molecules are candidates for use as building blocks of multidimensional switching devices because the π electrons can generate ring currents with a variety of directions. We employed (P)-2,2'-biphenol because four patterns of π-electron rotations along the two phenol rings are possible and theoretically determine how quantum switching of the π-electron rotations can be realized. We found that each rotational pattern can be driven by a coherent excitation of two electronic states under two conditions: one is the symmetry of the electronic states and the other is their relative phase. On the basis of the results of quantum dynamics simulations, we propose a quantum control method for sequential switching among the four rotational patterns that can be performed by using ultrashort overlapped pump and dump pulses with properly selected relative phases and photon polarization directions. The results serve as a theoretical basis for the design of confined ultrafast switching of ring currents of nonplanar molecules and further current-induced magnetic fluxes of more sophisticated systems.

Quantum computation with programmable connections between gates

A new model of quantum computation is considered, in which the connections between gates are programmed by the state of a quantum register. This new model of computation is shown to be more powerful than the usual quantum computation, e.g. in achieving the programmability of permutations of N different unitary channels with 1 use instead of N uses per channel. For this task, a new elemental resource is needed, the quantum switch, which can be programmed to switch the order of two channels with a single use of each one.

Measuring Entanglement Entropy of a Generic Many-Body System with a Quantum Switch

Entanglement entropy has become an important theoretical concept in condensed matter physics because it provides a unique tool for characterizing quantum mechanical many-body phases and new kinds of quantum order. However, the experimental measurement of entanglement entropy in a many-body system is widely believed to be unfeasible, owing to the nonlocal character of this quantity. Here, we propose a general method to measure the entanglement entropy. The method is based on a quantum switch (a two-level system) coupled to a composite system consisting of several copies of the original many-body system. The state of the switch controls how different parts of the composite system connect to each other. We show that, by studying the dynamics of the quantum switch only, the Rényi entanglement entropy of the many-body system can be extracted. We propose a possible design of the quantum switch, which can be realized in cold atomic systems. Our work provides a route towards testing the scaling of entanglement in critical systems as well as a method for a direct experimental detection of topological order.

Quantum conductance and switching kinetics of AgI-based microcrossbar cells

Microcrossbar structured electrochemical metallization (ECM) cells based on silver iodide (AgI) solid electrolyte were fabricated and analyzed in terms of the resistive switching effect. The switching behavior implies the existence of quantized conductance higher than 78 µS which can be identified as a multiple of the single atomic point contact conductivity. The nonlinearity of the switching kinetics has been analyzed in detail. Fast switching in at least 50 ns was observed for short pulse measurements.

A centralized quantum switch network based on probabilistic channels

We present a practical scheme for deterministically teleporting quantum information via probabilistic communication channels in a centralized quantum switch network. In the network, a central quant...

Improved Round Robin Scheduling using Dynamic Time Quantum

Round Robin scheduling algorithm is the widely used scheduling algorithm in multitasking and real time environment. It is the most popular algorithm due to its fairness and starvation free nature towards the processes, which is achieved by using the time quantum. As the time quantum is static, it causes less context switching incase of high time quantum and high context switching incase of less time quantum. Increasing context switch leads to high avg. waiting time, high avg. turnaround time which is a overhead and degrades the system performance. So, the performance of the system solely depends upon the choice of optimal time quantum which is dynamic in nature. In this paper, we have proposed a new variant of RR scheduling algorithm known as Improved Round Robin (IRR) Scheduling algorithm, by arranging the processes according to their shortest burst time and assigning each of them with an optimal time quantum which is able to reduce all the above said disadvantages. Experimentally we have shown that our proposed algorithm performs better than the RR algorithm, by reducing context switching, average waiting and average turnaround time.

Spin-polarized transport in a normal/ferromagnetic/normal zigzag graphene nanoribbon junction

We investigate the spin-dependent electron transport in single and double normal/ferromagnetic/normal zigzag graphene nanoribbon (NG/FG/NG) junctions. The ferromagnetism in the FG region originates from the spontaneous magnetization of the zigzag graphene nanoribbon. It is shown that when the zigzag-chain number of the ribbon is even and only a single transverse mode is actived, the single NG/FG/NG junction can act as a spin polarizer and/or a spin analyzer because of the valley selection rule and the spin-exchange field in the FG, while the double NG/FG/NG/FG/NG junction exhibits a quantum switching effect, in which the on and the off states switch rapidly by varying the cross angle between two FG magnetizations. Our findings may shed light on the application of magnetized graphene nanoribbons to spintronics devices.

Self-Routing Quantum Sparse Crossbar Packet Concentrators

Quantum switching networks are derived from conventional switching networks by replacing the classical switches by quantum switches. We give the quantum circuit design and routing of an n × m network, called a quantum concentrator that can direct quantum bit packets in arbitrary quantum states from any of its k inputs to some of its k outputs, where 1 ≤ k ≤ m ≤ n. Our designs are based on sparse crossbars which are rectangular grids of 2 × 2 crosspoints. Sparse crossbar concentrator structures with theoretically minimum crosspoint complexities for any values of n and m are well known but no self-routing algorithms have been reported for such concentrators. We transform two such families of optimal concentrators, called fat-slim and banded sparse crossbars into quantum networks and provide self-routing algorithms for these families of concentrators. In this process, we extend the notion of packet concentration to a quantum network and design self-routing quantum crosspoints from quantum gates. We address issues critical to quantum operation like reversibility and localized self-routing and give a rigorous proof that quantum fat-slim and banded sparse crossbar concentrators are self-routable. The self-routing algorithms described in the paper can be used for both quantum and classical sparse crossbar concentrators by the linearity property of all quantum systems.

Efficient quantum computing using coherent photon conversion

Single photons are excellent quantum information carriers: they were used in the earliest demonstrations of entanglement and in the production of the highest-quality entanglement reported so far. However, current schemes for preparing, processing and measuring them are inefficient. For example, down-conversion provides heralded, but randomly timed, single photons, and linear optics gates are inherently probabilistic. Here we introduce a deterministic process--coherent photon conversion (CPC)--that provides a new way to generate and process complex, multiquanta states for photonic quantum information applications. The technique uses classically pumped nonlinearities to induce coherent oscillations between orthogonal states of multiple quantum excitations. One example of CPC, based on a pumped four-wave-mixing interaction, is shown to yield a single, versatile process that provides a full set of photonic quantum processing tools. This set satisfies the DiVincenzo criteria for a scalable quantum computing architecture, including deterministic multiqubit entanglement gates (based on a novel form of photon-photon interaction), high-quality heralded single- and multiphoton states free from higher-order imperfections, and robust, high-efficiency detection. It can also be used to produce heralded multiphoton entanglement, create optically switchable quantum circuits and implement an improved form of down-conversion with reduced higher-order effects. Such tools are valuable building blocks for many quantum-enabled technologies. Finally, using photonic crystal fibres we experimentally demonstrate quantum correlations arising from a four-colour nonlinear process suitable for CPC and use these measurements to study the feasibility of reaching the deterministic regime with current technology. Our scheme, which is based on interacting bosonic fields, is not restricted to optical systems but could also be implemented in optomechanical, electromechanical and superconducting systems with extremely strong intrinsic nonlinearities. Furthermore, exploiting higher-order nonlinearities with multiple pump fields yields a mechanism for multiparty mediation of the complex, coherent dynamics.

Characterization of quantum conducting channels in metal/molecule/metal devices using pressure-modulated conductance microscopy

Nanoscale switches will play a crucial role in the design of future nanoelectronic circuits. An interesting candidate involves metal/molecule/metal structures that operate via modulation of nanoscale conducting channels. When the conductance falls in the ballistic regime between 1∼2G Q (where G Q =2e 2/h or ≈80 μS), resonant electron transport was observed in such devices at room temperature. By performing pressure-modulated conductance microscopy, we have characterized the quantum conducting channels in terms of the wave vector of the electrons. We also observed two-level fluctuations in conductance, with each level showing opposite pressure responses, confirming the existence of resonant electron transport. These observations could lead to a new type of high speed quantum switching device based on electron wave interference.

Quantum Switching Based on the Nearest Neighbor Hamiltonian

This paper describes a quantum switching architecture for nearest neighbor coupling. An efficient quantum shear sorting (QSS) algorithm is used to reduce the number of time steps. For the QSS algorithm, the running complexity of the quantum switching architecture is polynomial in time with the nearest neighbor coupling and the implementation is less complex. The result shows that improved switching is extremely simple to implement using existing quantum computer candidates.

Quantum teleportation internetworking and routing strategy

The principle of the quantum switch is introduced by means of entanglement swapping. With the help of quantum switch operating entanglement swapping one by one, quantum correlations between Alice and Bob can be established. Adding entangled particle generator into conventional interconnection equipments, such as switch, and keeping quantum correlations between adjacent devices in the network leisure time, one can upgrade the classic internet to quantum teleportation internet. In quantum teleportation internet, the routing is selected also by utilizing the routing algorithm of classical internet. The routing selection can be synchronized with the establishment of quantum channel in static routing strategy. When the dynamic routing strategy is selected, quantum switch first selects a route to generate a router sequence table and then operates entanglement swapping one by one according to the table to establish the quantum correlations between Alice and Bob.

Interaction-free all-optical switching in χ^(2)microdisks for quantum applications

We propose a quantum switch for telecom-band applications that is composed of a chi((2)) microdisk coupled to two fibers (or waveguides). The idea is to apply a pump pulse to shift the microdisk out of resonance, thereby switching the device between the cross and bar states in an interaction-free manner. As an example, a 2.5-microm-thick, 10 microm radius GaAs microdisk with an intrinsic Q of approximately 10(8) and a fiber-cavity-coupling Q of approximately 10(4) can achieve low-loss (< or approximately equal to 1%) switching for gigahertz-rate O-band quantum signals with milliwatt-peak-power pumps in the C band.

Magnetotransport in a time-modulated double quantum point contact system

We report on a time-dependent Lippmann–Schwinger scattering theory that allows us to study the transport spectroscopy in a time-modulated double quantum point contact system in the presence of a perpendicular magnetic field. Magnetotransport properties involving inter-subband and inter-sideband transitions are tunable by adjusting the time-modulated split-gates and the applied magnetic field. The observed magnetic field induced Fano resonance feature may be useful for the application of quantum switching.

Two-resonator circuit quantum electrodynamics: Dissipative theory

We present a theoretical treatment for the dissipative two-resonator circuit quantum electrodynamics setup referred to as quantum switch. There, switchable coupling between two superconducting resonators is mediated by a superconducting qubit operating in the dispersive regime, where the qubit transition frequency is far detuned from those of the resonators. We derive an effective Hamiltonian for the quantum switch beyond the rotating wave approximation and study the dissipative dynamics within a Bloch-Redfield quantum master equation approach. We derive analytically how the qubit affects the quantum switch even if the qubit has no dynamics, and we estimate the strength of this influence. The analytical results are corroborated by numerical calculations, where coherent oscillations between the resonators, the decay of coherent and Fock states, and the decay of resonator-resonator entanglement are studied. Finally, we suggest an experimental protocol for extracting the damping constants of qubit and resonators by measuring the quadratures of the resonator fields.

Generation of remote multi-photon entangled state from Einstein–Podolsky–Rosen photon pairs

We describe a protocol for generation of remote multi-photon entanglement using Einstein–Podolsky–Rosen (EPR) photon pairs via entanglement swapping. According to the requests of users, Quantum Switch (QS) can prepare three-photon W entangled states or Greenberger–Horne–Zeilinger (GHZ) states based on independent, spatially separated EPR pairs among three distant users. Only Bell states measurement (BSM) is needed utilizing a CPHASE gate and PAs. This protocol can also generate remote N-photon GHZ entangled states.

Scattering of two coherent photons inside a one-dimensional coupled-resonator waveguide

We consider the coherent propagation of n photons in a one-dimensional coupled-resonator waveguide for n=2,3,4.... The scattering by a three-level atom, which resides in one of the resonators of the waveguide and gives rise to only two-photon transitions, results in a perfect quantum switch that allows either total reflection or total transmission. This is to be contrasted to the case of a single photon inside a one-dimensional resonant waveguide scattered by a two-level system with single-photon transitions where only total reflection can be accomplished; viz. the system behaves only as a perfect mirror but not as an ideal, transparent medium.

Quantum Zeno switch for single-photon coherent transport

Using a dynamical quantum Zeno effect, we propose a general approach to control the coupling between a two-level system (TLS) and its surroundings, by modulating the energy level spacing of the TLS with a high frequency signal. We show that the TLS--surroundings interaction can be turned on or off when the ratio between the amplitude and the frequency of the modulating field is adjusted to be a zero of a Bessel function. The quantum Zeno effect of the TLS can also be observed by the vanishing of the photon reflection at these zeros. Based on these results, we propose a quantum switch to control the transport of a single photon in a 1D waveguide. Our analytical results agree well with numerical results using Floquet theory.

Anomalous Kondo-Switching Effect of a Spin-Flip Quantum Dot Embedded in an Aharonov–Bohm Ring

We theoretically investigate the Kondo effect of a quantum dot embedded in a mesoscopic Aharonov–Bohm (AB) ring in the presence of the spin flip processes by means of the one-impurity Anderson Hamiltonian. Based on the slave-boson mean-field theory, we find that in this system the persistent current (PC) sensitively depends on the parity and size of the AB ring and can be tuned by the spin-flip scattering (R). In the small AB ring, the PC is suppressed due to the enhancing R weakening the Kondo resonance. On the contrary, in the large AB ring, with R increasing, the peak of PC firstly moves up to max-peak and then down. Especially, the PC phase shift of π appears suddenly with the proper value of R, implying the existence of the anomalous Kondo effect in this system. Thus this system may be a candidate for quantum switch.