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Charge State Manipulation of Qubits in Diamond


Charge State Manipulation of Qubits in Diamond

Bernhard Grotz et al. Nat Commun.


The nitrogen-vacancy (NV) centre in diamond is a promising candidate for a solid-state qubit. However, its charge state is known to be unstable, discharging from the qubit state NV(-) into the neutral state NV(0) under various circumstances. Here we demonstrate that the charge state can be controlled by an electrolytic gate electrode. This way, single centres can be switched from an unknown non-fluorescent state into the neutral charge state NV(0), and the population of an ensemble of centres can be shifted from NV(0) to NV(-). Numerical simulations confirm the manipulation of the charge state to be induced by the gate-controlled shift of the Fermi level at the diamond surface. This result opens the way to a dynamic control of transitions between charge states and to explore hitherto inaccessible states, such as NV(+).


Figure 1
Figure 1. Electrical manipulation of the charge state of NV centres in diamond.
(a) Sketch of the experimental configuration showing the shallow-implanted NV centres in the O/H-patterned diamond surface. (b) Energy band schematic of the diamond/electrolyte interface. By applying a gate voltage between the gate electrode and H-terminated diamond, it is possible to control the Fermi energy level, moving it through the charge transition levels NV+/0 and NV0/−. (c) Fluorescence image of an O/H-patterned diamond with shallow-implanted NV centres under floating gate conditions. Regions 1 and 2 indicate areas with low and high dose of NVs, respectively. (d) Time trace of the fluorescence intensity upon changes between UG=±0.5 V (650 nm longpass filter) recorded on region (2).
Figure 2
Figure 2. Gate-dependent spectral properties of NV centres.
(a) Spectra of the H-terminated area of a 10 keV implantation in a region with high implantation density (black: UG=+0.5 V, red: UG=−0.5 V). ZPL, zero-phonon-line. (bd) Difference of the spectra at UG=+0.5 V and UG=−0.5 V ((b) at ∼1013 cm−2, (c) at ∼1012 cm−2 and (d) at ∼1011 cm−2). The dashed line indicates zero level. (e) Difference spectrum of a single NV centre (implantation density ∼1011 cm−2) when switching from UG=+0.4 V to UG=−0.4 V. The dashed line indicates zero level.
Figure 3
Figure 3. Charge state control of single NV centres.
(a) Fluorescence image of a 5 keV spot in a hydrogenated region at gate potential UG=0.5 V, bar indicates 1 μm. (b) Selected centres at various gate voltages. (c) Number of NV centres visible in the scanned region of (a) at different gate voltages. (d) Photon statistics g(2)(τ) measured on a single centre (background corrected, UG=0.5 V). (e,f) Gate-voltage dependence of the fluorescence intensity of two single NV centres.
Figure 4
Figure 4. Simulation of the energy band structure of H-terminated diamond in contact with an electrolyte.
(a) At UG=−0.5 V (red), the Fermi level EF (dash-dotted line) crosses the charge transition level NV+/0 (dashed line) much deeper in the diamond as compared with UG=+0.5 V (blue). (b) At negative UG, the Fermi level lies below the VBM (solid line) in the surface region, inducing a two-dimensional hole gas (2-DHG; blue area). (c) Energy band schematic showing the intersection of the Fermi level with the NV+/0 level at UG=0.3 V and UG=0.4 V. The density profile of neutrally charged NV is shown in comparison with the implantation. (d) Simulated fraction of neutrally charged NV versus the gate voltage. (e) VBM and the NV+/0 (dashed lines), as well as the NV0/− charge transition levels (dotted line), are shown for two different implantation dose (1012 and 1013 cm−2). The background nitrogen concentration is 50 p.p.b. The implantation density profile for 10 keV is shown for reference.

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