A photonic quantum gate based on electrically controlled strong cavity coupling between a single nanocrystal quantum dot and an ultra-high Q silica micro-cavity

We investigate the use of nanocrystal quantum dots as a versatile quantum bus element for preparing various quantum resources for use in photonic quantum technologies. The ability to Stark tune nanocrystal quantum dots allows an important degree of control over the cavity QED interaction. Using this property along with the bi-exciton transition, we demonstrate a photonic CNOT interaction between two logical photonic qubits comprising two cavity field modes each. We find the CNOT interaction to be a robust generator of photonic Bell states, even with relatively large bi-exciton losses.These results are discussed in light of the current state-ofthe-art of both microcavity fabrication and recent advances in nanocrystal quantum dot technology. Overall, we find that such a scheme should be feasible in the near future with appropriate refinements to both nanocrystal fabrication technology and micro-cavity design. Such a gate could serve as an active element in photonic-based quantum technologies

Charge hopping revealed by jitter correlations in the photoluminescence spectra of single CdSe nanocrystals

Spectral fluctuations observed in single CdSe/ZnS nanocrystals at 5 K are found to be entirely the result of discrete charge hops in the local environment of the nanocrystal, which occur at a rate comparable to the acquisition time of a single spectrum. We show that intervals between discrete spectral hops introduce a correlation between the successive measurements of the emission wavelength of single CdSe nanocrystals. This correlation can be recovered even in the presence of noise, but is shown to be sensitive to the experimental acquisition time, in good agreement with theory. However, we only find correlations for the smaller of the two nanocrystal sizes studied and discuss this in terms of size-dependent time scales correlated with the amount of excess energy dissipated in the nanocrystal due to hot-carrier relaxation. © 2010 The American Physical Societ

Evidence for energy relaxation via a radiative cascade in surface-passivated PbS quantum dots

Multiple emission peaks have been observed from surface passivated PbS nanocrystals displaying strong quantum confinement. The emission spectra are shown to be strongly dependent on the excited-state parity. We also find that intraband energy relaxation from initial states excited far above the band-edge is nearly three orders of magnitude slower than that found in other nanocrystal quantum dots, providing evidence of inefficient energy relaxation via phonon emission. The initial-state parity dependence of the photoluminescent emission properties suggests that energy relaxation from the higher excited states occurs via a radiative cascade, analogous to energy relaxation in atomic systems. Such radiative cascade emission is possible from ideal zero-dimensional semiconductors, where electronic transitions can be decoupled from phonon modes

Direct observation of mixed-parity excited states in surface-passivated PbS nanocrystals

Photoluminescent emission is observed from surface-passivated PbS nanocrystals following the two-photon excitation of high-energy excitonic states. The emission appears directly at the excitation energy with no detectable Stokes-shift for a wide range of excitation energies. The observation of direct emission from states excited by two-photon absorption indicates that the parity of the excited states of surface-passivated PbS nanocrystals is partially mixed