QUIE2T Quantum Information Entanglement-Enabled Technologies

The nitrogen-vacancy (NV) center in diamond is supposed to be a building block for quantum computing and nanometer-scale metrology at ambient conditions. Therefore, precise knowledge of its quantum states is crucial. Here, we experimentally show that under usual operating conditions the NV exists in an equilibrium of two charge states [70% in the expected negative (NV-) and 30% in the neutral one (NV0)].

Fluorescent particles are routinely used to probe biological processes1. The quantum properties of single spins within fluorescent particles have been explored in the field of nanoscale magnetometry

Diamond spins are an ideal test bed for exploring quantum physics of few well controllable qubit systems. Defect center electron spins show strong coupling to a light field and at the same time interact with few surrounding nuclei in the lattice. As a result the system usually constitutes a few qubit system with excellent coherence and controllability even at room temperature. It fulfills all characteristics of a quantum register including single shot read-out capability.

Diamond defects allow for precise measurement of single electron and nuclear spin quantum states. The excellent controllability of these spins as well as efficient decoupling from environment make them an ideal playground for engineering complex quantum states and development of elaborate control schemes. The talk will describe how nuclear spin states can be efficiently read-out and used as Qbits in spin clusters. Routes towards the controlled engineering of extended spin arrays as well as coupling to control structures will be discussed.

Interaction of defect centers in diamond and molecules with thin metal wires, bow tie, and other antenna structures: By studying the coupling efficiency and mechanism we achieve an improved insight into the quantum plasmon interaction.

SOLID members from the Kavli Institute at TU-Delft have shown how spin-orbit interaction provides a way to control spins electrically. A spin–orbit quantum bit (qubit) is electrostatically defined in an indium arsenide nanowire, where the spin–orbit interaction is so strong that spin and motion can no longer be separated. In this regime, the group has realized fast qubit rotations and universal single-qubit control using only electric fields; the qubits are hosted in single-electron quantum dots that are individually addressable.

Amongst all the microscopic quantum spin systems that can be coupled to superconducting circuits, negatively charged nitrogen- vacancy centers (N-V) in diamond are particularly attractive. One of the major reasons is that the spin coherence time has been shown to be as long as 2ms at room temperature. Compared to atoms, N-V centers are perfectly compatible with superconducting circuits, because they do not require challenging trapping techniques or large magnetic fields to bring them in resonance at GHz frequency with the circuit.

The Karlsruhe groups of A. Ustinov and A. Shnirman (KTA) have demonstrated a new method to directly manipulate the state of individual two-level systems (TLSs) in phase qubits. The method allows one to characterize the coherence properties of TLSs using standard microwave pulse sequences, while the qubit is used only for state readout. The group has applied this method to perform the first measurement of the temperature dependence of TLS coherence.