***NON-TECHNICAL ABSTRACT*** A quantum dot is a nanoscale chunk of one semiconductor material inside of another, which acts as a box for the electrons within it, while an optical nanocavity resonantly recirculates light inside of its nanoscale volume. It has recently been shown that a system consisting of a single quantum dot embedded inside of an optical nanocavity can be employed as a practical platform to study various new regimes of interaction between light and matter, even at a level of only one particle of light called photon. This single investigator proposal focuses on performing a series of experiments on this platform, including the observation of true quantum mechanical states of coupled light and matter (called the dressed states), photon blockade (the regime in which the presence of one photon inside of a nanocavity prohibits another photon from entering it), and the controlled interaction between only two photons mediated by such a system (controlled phase shift). In addition to probing new regimes of quantum and nanoscale physics, this system can be used to develop a more practical platform for quantum communication and quantum computing - systems based on powerful properties of quantum mechanics which have the potential to revolutionize information technology, security, and even drug discovery. Over the course of this project, a number of students will be trained in state of the art optical techniques, and will gain expertise in an area that bridges many disciplines of physics and engineering, which will prepare them for work in academia, industry or government. The project receives support from the Divisions of Materials Research and Physics.
Solid-state cavity quantum electrodynamics (QED) systems based on photonic crystal nanocavities and semiconductor quantum dots have seen rapid progress. Recent photoluminescence experiments have led to the observation of weak and strong coupling regimes of light-matter interaction. In addition, resonant light scattering has provided a means to directly probe cavity-quantum dot coupling. This single investigator project focuses on probing the quantum states of light, as well as cavity QED, in such a solid state system. In order to obtain an improved understanding of light-matter interactions, the project will attempt to observe dressed states of the cavity QED system, photon blockade, and controlled phase shifts at a single photon level (i.e., a nonlinear interaction between two individual photons mediated by such a system). In addition, the system can be used to develop a more practical platform for quantum communication and quantum computing, as well as for ultra low power all-optical computing. Over the course of this project, a number of students will be trained in state of the art optical techniques, and will gain expertise in an area that bridges many disciplines of physics and engineering, ranging from quantum optics, quantum information science, and mesoscopic physics, to photonics and optoelectronics. The project receives support from the Divisions of Materials Research and Physics.
Nanophotonic structures can be employed as a more practical testbed for fundamental experiments on light-matter interaction (a field known as cavity quantum electrodynamics, or cavity QED). As opposed to the atomic cavity QED platform on which such experiments have been explored for the past 30 years, we use a solid-state platform, which enables a much smaller, on-chip, scalable, and simpler system: we employ InAs quantum dots which are already naturally trapped inside the GaAs nano-resonator material. In addition, as a result of the ultra-small optical volumes, the interaction strength between the quantum dot and the cavity field in our system is in the range of several 10's of GHz - three orders of magnitude higher than for the previous atomic systems. Therefore, everything happens much faster as well. The practicality and speed make these structures also interesting as a platform for a new generation of classical and quantum information processing devices. One of the key properties of the system consisting of a single quantum dot strongly coupled to a resonator is that the presence of the dot can completely modify the optical transmission through such a structure, from transparent to opaque for an optical beam on resonance. This could be done at a rate proportional to the coupling strength between the emitter and the field (i.e., 10's of GHz for the quantum dot-nanocavity system, as opposed to MHz in the atom-cavity system), opening up opportunities to build practical devices, such as fast, all-optical switches operating at the single photon level. In addition to the potential for improving the properties of conventional optoelectronic devices (such as optical switches), nanophotonics is a viable candidate for building circuits for quantum information processing which employ the quantum mechanical properties of matter and light. Applications of interest include quantum networks and repeaters (that would enable secure transmission of information over large distances), as well as quantum simulators which would enable studies of complex physical processes by constructing analogous, more easily controllable systems. Over the course of this project, we have worked on the development and study of the quantum dot-photonic crystal cavity QED platform. Some of our most important results include the demonstration of controlled switching between two optical pulses at the single photon level mediated by such a platform [Physical Review Letters 108, 093604 (2012)], and an extension of this platform to the system of coupled resonators with quantum emitters inside of them, which would be useful for quantum simulation [Physical Review B 86, 045315 (2012), Physical Review B 86, 195312 (2012) – see Figure 1]. In addition to the significant research results described above, the project has also made significant contributions to education and human resources, as well as resources for science and technology. A number of students from our group and outside have been trained to perform these experiments (we have even introduced a similar experiment in the photonics laboratory class taught at Stanford). In addition to the PI, several of the graduate students involved with this project have been women. Finally, a couple of graduate students who worked on this project have joined leading universities as assistant professors.
