Strong interactions between single spins and photons are essential for quantum networks and distributed quantum computation. They provide the necessary interface for entanglement distribution, non-destructive quantum measurements, and strong photon-p
hoton interactions. Achieving spin-photon interactions in a solid-state device could enable compact chip-integrated quantum circuits operating at gigahertz bandwidths. Many theoretical works have suggested using spins embedded in nanophotonic structures to attain this high-speed interface. These proposals exploit strong light-matter interactions to implement a quantum switch, where the spin flips the state of the photon and a photon flips the spin-state. However, such a switch has not yet been realized using a solid-state spin system. Here, we report an experimental realization of a spin-photon quantum switch using a single solid-state spin embedded in a nanophotonic cavity. We show that the spin-state strongly modulates the cavity reflection coefficient, which conditionally flips the polarization state of a reflected photon on picosecond timescales. We also demonstrate the complementary effect where a single photon reflected from the cavity coherently rotates the spin. These strong spin-photon interactions open up a promising direction for solid-state implementations of high-speed quantum networks and on-chip quantum information processors using nanophotonic devices.
We propose a method to read-out the spin-state of an electron in a quantum dot in a Voigt geometry magnetic field using cycling transitions induced by the AC Stark effect. We show that cycling transitions can be made possible by a red-detuned, circul
arly-polarized laser, which modifies the spin eigenstates and polarization selection rules via the AC Stark effect. A Floquet-Liouville supermatrix approach is used to calculate the time-evolution of the density matrix under the experimental conditions of a spin read-out operation. With an overall detection efficiency of 2.5%, the read-out is a single-shot measurement with a fidelity of 76.2%.
We demonstrate reversible strain-tuning of a quantum dot strongly coupled to a photonic crystal cavity. We observe an average redshift of 0.45 nm for quantum dots located inside the cavity membrane, achieved with an electric field of 15 kV/cm applied
to a piezo-electric actuator. Using this technique, we demonstrate the ability to tune a quantum dot into resonance with a photonic crystal cavity in the strong coupling regime, resulting in a clear anti-crossing. The bare cavity resonance is less sensitive to strain than the quantum dot and shifts by only 0.078 nm at the maximum applied electric field.
We present a method to control the resonant coupling interaction in a coupled-cavity photonic crystal molecule by using a local and reversible photochromic tuning technique. We demonstrate the ability to tune both a two-cavity and a three-cavity phot
onic crystal molecule through the resonance condition by selectively tuning the individual cavities. Using this technique, we can quantitatively determine important parameters of the coupled-cavity system such as the photon tunneling rate. This method can be scaled to photonic crystal molecules with larger numbers of cavities, which provides a versatile method for studying strong interactions in coupled resonator arrays.
The 4-bar crystal symmetry in materials such as GaAs can enable quasi-phasematching for efficient frequency conversion without poling, twinning or other engineered domain
We demonstrate a method of tuning a semiconductor quantum dot (QD) onto resonance with a cavity mode all-optically. We use a system comprised of two evanescently coupled cavities containing a single QD. One resonance of the coupled cavity system is u
sed to generate a cavity enhanced optical Stark shift, enabling the QD to be resonantly tuned to the other cavity mode. A twenty-seven fold increase in photon emission from the QD is measured when the off-resonant QD is Stark shifted into the cavity mode resonance, which is attributed to radiative enhancement of the QD. A maximum tuning of 0.06 nm is achieved for the QD at an incident power of 88 {mu}W.
We experimentally investigate the dynamic nonlinear response of a single quantum dot (QD) strongly coupled to a photonic crystal cavity-waveguide structure. The temporal response is measured by pump-probe excitation where a control pulse propagating
through the waveguide is used to create an optical Stark shift on the QD, resulting in a large modification of the cavity reflectivity. This optically induced cavity reflectivity modification switches the propagation direction of a detuned signal pulse. Using this device we demonstrate all-optical switching with only 14 attojoules of control pulse energy. The response time of the switch is measured to be up to 8.4 GHz, which is primarily limited by the cavity-QD interaction strength.
We compare the photoluminescence spectrum of an indium arsenide (InAs) quantum dot (QD) that is strongly coupled to a photonic crystal cavity under above band excitation (ABE) and quasi-resonant excitation (QRE). We show that off-resonant cavity feed
ing, which manifests itself in a bare cavity emission peak at the strong coupling point, is suppressed by as much as 40% under QRE relative to ABE. We attribute this suppression to a reduced probability of QD charging because electrons and holes are created in pairs inside the QD. We investigate the pump power dependence of the cavity feeding and show that, below saturation, the ratio of the bare cavity emission to polariton emission for ABE is independent of pump power, while for QRE there is linear pump power dependence. These results suggest that the biexciton plays an important role in cavity feeding for QRE.
