Developing small-scale quantum information processors based on electronic spins in diamond.
Abstract: Isolated optically-active solid-state spins such as the Nitrogen-Vacancy (NV) center in diamond have demonstrated good properties as qubits for quantum information processing tasks. However, engineering a quantum register of spins around a central NV qubit enables more powerful applications. For example, given their weak coupling to the environment a register of nuclear spins has demonstrated enhanced quantum memory, quantum error correction, and many interesting quantum protocols. Still, thanks to their stronger coupling between spins and to external fields, a register of electronic spins would enable new complementary applications, especially in the areas of quantum sensing and quantum device characterization.
In this talk I will present three critical steps towards developing a small-scale quantum information processor based on electronic spins in diamond.
First, we demonstrate an approach to systematically build up a system of interacting electronic spins starting from a central NV qubit. Concretely, we develop a general method to characterize the Hamiltonian of an unknown interacting spin system via sweep of an external magnetic field, and applying this characterize two unknown optically-dark electron-nuclear spin defects around our NV. Thus the approach allows not only identification of spin defects at the single-molecular level but also coherent control of the multi-qubit system [1].
We then turn our attention to the environment surrounding our electronic spin register which causes decoherence (noise). Here, inspired the method of quantum noise spectroscopy, we demonstrate a practical approach to build a predictive noise model of qubit dephasing. Thus characterizing the noise of our nanoscale two-qubit system we surprisingly find a spatially non-uniform and complex quantum spin environment. Extending to multi-qubit devices this approach may be of interest for quantum sensing many-body environments with high spatial resolution, developing tailored dynamical decoupling sequences to extend the coherence time, and characterizing correlated noise between qubits for quantum error correction [2].
Finally, to highlight a potential advantage of electronic spin registers we demonstrate a path to achieve practical quantum advantage in a particular quantum information task of interest, namely in sensing of external classical fields. Concretely, to overcome the higher overhead associated with entanglement-enhanced sensing (due to more complex quantum circuits to generate and detect entanglement and faster decoherence), using a two-qubit system we demonstrate a novel sensing protocol to enhance the sensitivity via both entanglement and repetitive readout of a quantum memory [3].
[1] A. Cooper, W. K. C. Sun, J.C. Jaskula, and P. Cappellaro, Physical Review Letters 124, 083602 (2020).
[2] W. K. C. Sun, P. Cappellaro, Physical Review B 106, 155413 (2022).
[3] A. Cooper, W. K. C. Sun, J.C. Jaskula, and P. Cappellaro, Physical Review Applied 12, 044047 (2019).
