Spin Quantum Computing

David Peter Divincenzo

Anant Aravind Kulkarni, Sanjay Prajapati, Shivam Verma +1 more

The semiconductor industry is facing a twofold challenge at sub-nanometer level; first, the high power dissipation in irreversible computing architectures due to information loss and second, inability to handle large data due to sequential information processing. These issues create obstacles in producing the presumed low-power complex computing outcomes. The heat dissipation can be reduced by utilizing the complementary metal-oxide-semiconductor-based reversible computing architectures. However, these architectures fail to enhance the performance owing to inability to process large data. Quantum computing (QC) can circumvent these problems due to its fundamental ineffaceable characteristics of quantum mechanics-based reversible computing and parallelism. Spin-torque-based physical realization is the most suitable platform for reversible computing due to the electron spin analogous to the qubit. However, optimal quantum circuits are required to physically realize the complex Boolean logic due to spin-qubit decoherence and reduce the number of transistor switching activities for the spin generation and injection required for the spin-qubit rotation. Therefore, in this paper, optimal quantum circuit decompositions are presented with the help of developed elementary quantum library {Ry(θ), Rz(θ), √SWAP for the spin-torque-based QC architecture. The reversible Boolean logic performance is analyzed and compared for the conventional, reduced, and optimal decompositions on the first- and second-order transmission coefficient matrix-based spin-torque QC architecture. The results encourage to set a path toward QC-based reconfigurable complex computing systems in near future.

M. Tei, Yoichi Mizuno, Yoshinori Manmoto +2 more

Abstract Recently, quantum algorithms have been realized on a quantum computer by using a nuclear magnetic resonance technique. The nuclear magnetic resonance quantum computer (NMR‐QC) consists of nuclear spins of molecules that are coupled by J‐coupling to each other and the nuclear spins take a role of quantum bits (qubits). In performing quantum algorithms on NMR‐QC, the decoherence effects are a key problem. We studied the decoherence effects in the four‐qubit NMR‐QC using the fluorine nuclear spins of tetrafluoropyridine molecules. The nitrogen nuclear spin in the tetrafluoropyridine molecule increases the transverse relaxation rate of nearby fluorine nuclear spins about 10 times because of its quadrupole moment. In this study we evaluated the decoherence effects in the NMR‐QC by utilizing controlled‐not quantum gates. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003

Antoon Hendrik Hams

Niklas Rohling, Maximilian Rimbach-Russ, Guido Burkard

The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.

David Peter Divincenzo, Guido Burkard, Daniel Loss +1 more