Manipulating quantum information with spin torque

Abstract

The use of spin torque as a substitute for magnetic fields is now well established for classical operations like the switching of a nanomagnet. What we are describing here could be viewed as an application of spin torque like effects to quantum processes involving single qubit rotations as well as two qubit entanglement. A key ingredient of this scheme is the use of a large number of itinerant electrons whose cumulative effect is to produce the desired qubit operations on static spins. Each interaction involves entanglement and collapse of wavefunctions so that the operation is only approximately unitary. However, we show that the non-unitary component of the operations can be kept below tolerable limits with proper design. As a capstone example, we present the implementation of a complete CNOT gate using the proposed spin potential based architecture, and show that the fidelity under ideal conditions can be made acceptably close to one.

Collision models in quantum optics

“…This is neither awkward nor trivial, as recently highlighted in Refs. [50,52], and can give rise to appealing applications such as the implementation of one-and two-qubit quantum gates [53]. In order for the dissipator in Eq.…”

Spin-torque oscillation in a magnetic insulator probed by a single-spin sensor

“…Thus in future work, NV sensors should be able to probe the sub-Hz regime of STO behavior [3], comparable to the capability of state-of-the-art electrical detection [37], combined with nanoscale spatial characterization of STO-generated magnetic fields [12,13], which is unavailable to electrical detection. Spatial mapping at such length scales would provide access to locations of large STO magnetic-field intensity, with the potential to use an STO to drive magnetic excitations in other systems of interest, such as spin waveguides [38] and spin qubits [39]. Finally, studies of spin-torque oscillation may provide insight into phenomena such as magnon thermodynamics [40], strongly correlated many-body physics [22], and control over magnetic phase transitions [41]…”

Quantum collision models: Open system dynamics from repeated interactions

“…Particular attention was given to the regime of ultra-short collision times yielding a unitary dynamics (as we discussed). This paradigm of unitary CM was proposed to carry out indirect quantum control [69] and universal two-qubit quantum gates in spintronics systems [70].…”