Robabeh Rahimi

Molecular electron-spin quantum computers and quantum information processing: pulse-based electron magnetic resonance spin technology applied to matter spin-qubits

Pulse-based Electron–Nuclear and ELectron–electron DOuble Resonance (ENDOR/ELDOR) techniques have been applied to molecular spins in order to implement ensemble electron spin-qubit based quantum computers/computing (QC) and quantum information processing (QIP) in the solid state. Pulsed ENDOR-based QC/QIP experiments for super dense coding (SDC) have for the first time been carried out by the use of molecular electron- and nuclear-spin entities such as the stable malonyl radical as matter spin-qubits. The spin-qubit manipulation technology for quantum gate operations in this work is based on the time-proportional-phase-increment (TPPI) technique, enabling us to distinguish between the phases of spin-qubit based entangled states. The TPPI technique, as firstly applied by Mehring et al. (M. Mehring, J. Mende and W. Scherer, Phys. Rev. Lett., 2003, 90, 153001), has illustrated the establishment of quantum entanglement between electron- and nuclear-spin states and mutual interconversion between the electron–nuclear Bell states. The electron-spin 4π-periodicity in phase shows up in the QC/QIP experiments, explicitly and experimentally illustrating the electron-spin spinor nature for the first time. Tripartite QC experiments have been made, showing the occurrence of separable states. Also, the development of novel electron-spin technology to manipulate multi-electron spin-qubits is described. In this work, the pulsed coherent-dual ELDOR for QC/QIP has for the first time been implemented by invoking a novel microwave dual phase-rotation technique. Thus, applications of the coherent-dual ELDOR to molecular electron spin-qubit systems are also discussed, emphasising designing the molecular two electron-qubit systems appropriate for QC/QIP. g- and/or hyperfine A-tensor engineering approaches give us the two- and multi-electron-qubit systems, which have been a materials challenge to implement matter spin-qubit based QC/QIP. The targeted matter spin-qubits can be used to facilitate selective resonant microwave excitations achieved by the pulsed ELDOR technique. In addition to DiVincenzos five criteria, general requisites for scalable electron spin-qubit systems as 1D periodic robust spin structures are described. According to the requisites, double- or triple-stranded helicates embedding open-shell metal cations are proposed instead of organic molecular spin-qubits.

A Synthetic Two-Spin Quantum Bit: g-Engineered Exchange-Coupled Biradical Designed for Controlled-NOT Gate Operations†

A quantum gate: A system of two coupled electron spins that is useful for simple quantum computing operations has been prepared by synthesis of a biradical 1 and co-crystallization with an isomorphous host molecule. The two weakly exchange-coupled quantum bits (target qubit blue and control qubit red) span four electron spin states. The electron spin transition is denoted by two black arrows.

Nonclassical correlation in a multipartite quantum system: Two measures and evaluation

There is a commonly recognized paradigm in which a multipartite quantum system described by a density matrix having no product eigenbasis is considered to possess nonclassical correlation. Supporting this paradigm, we define two entropic measures of nonclassical correlation of a multipartite quantum system. One is defined as the minimum uncertainty about a joint system after we collect outcomes of particular local measurements. The other is defined by taking the maximum over all local systems about the minimum distance between a genuine set and a mimic set of eigenvalues of a reduced density matrix of a local system. The latter measure is based on an artificial game to create mimic eigenvalues of a reduced density matrix of a local system from eigenvalues of a density matrix of a global system. Numerical computation of these measures for several examples is performed.

Pseudo-entanglement evaluated in noninertial frames

Abstract We study quantum discord, in addition to entanglement, of bipartite pseudo-entanglement in noninertial frames. It is shown that the entanglement degrades from its maximum value in a stationary frame to a minimum value in an infinite accelerating frame. There is a critical region found in which, for particular cases, entanglement of states vanishes for certain accelerations. The quantum discord of pseudo-entanglement decreases by increasing the acceleration. Also, for a physically inaccessible region, entanglement and nonclassical correlation are evaluated and shown to match the corresponding values of the physically accessible region for an infinite acceleration.

PULSED ENDOR-BASED QUANTUM INFORMATION PROCESSING

Pulsed Electron Nuclear DOuble Resonance (pulsed ENDOR) has been studied for realization of quantum algorithms, emphasizing the implementation of organic molecular entities with an electron spin and a nuclear spin for quantum information processing. The scheme has been examined in terms of quantum information processing. Particularly, superdense coding has been implemented from the experimental side and the preliminary results are represented as theoretical expectations.

A quantum genetic algorithm with quantum crossover and mutation operations

In the context of evolutionary quantum computing in the literal meaning, a quantum crossover operation has not been introduced so far. Here, we introduce a novel quantum genetic algorithm that has a quantum crossover procedure performing crossovers among all chromosomes in parallel for each generation. A complexity analysis shows that a quadratic speedup is achieved over its classical counterpart in the dominant factor of the run time to handle each generation.

Hyperfine spin qubits in irradiated malonic acid: heat-bath algorithmic cooling

The ability to perform quantum error correction is a significant hurdle for scalable quantum information processing. A key requirement for multiple-round quantum error correction is the ability to dynamically extract entropy from ancilla qubits. Heat-bath algorithmic cooling is a method that uses quantum logic operations to move entropy from one subsystem to another and permits cooling of a spin qubit below the closed system (Shannon) bound. Gamma-irradiated,

EVALUATING MEASURES OF NONCLASSICAL CORRELATION IN A MULTIPARTITE QUANTUM SYSTEM

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