Nanoparticle coupled to waveguide

Nanotechnology and quantum information technology are emerging branches of science that involve the design of extremely small electronic and optical circuits that are built at the molecular level. Traditional opto-electronic circuits are fabricated using semiconductor wafers to form chips. Circuits are etched into the semiconductor wafers or chips. The etching process removes material from certain regions or layers of the chips. In contrast, nanotechnology generally deals with devices built upward by adding material, often a single atom at a time. This technique results in a device where every particle could have a purpose. Thus, extremely small devices, much smaller than devices formed by etching, are possible. For example, a logic gate could be constructed from only a few atoms. An electrical conductor can be built from a “nanowire” that is a single atom thick. A bit of data could be represented by the presence or absence of a single proton.

Quantum information technology provides a new avenue for creating smaller and potentially more powerful computers. Scientific theories such as quantum superposition and quantum entanglement are now being used to explore the possibility of creating smaller, more powerful computing devices. The development in this field has led to the use of light particles, or photons, to convey information. Light can be polarized into various states (e.g., horizontally polarized, vertically polarized) and can also exist in various momentum and frequency states. Exploiting these properties allows a single photon to represent a single quantum bit of information.

The use of quantum bits provides researchers with significant potential advancements in computing technology. The ability to understand and utilize the theories of photon superposition and entanglement to generate information is a new field around which there is significant interest. However, one important issue that surrounds potential use of photons as quantum bits is the need to generate a photon on demand at the location where it is desired. A second important issue is the ability to detect and capture the photons; that is, to efficiently collect light emitted from the photon source. Both of the foregoing attributes are useful in creating single-photon sources and nonlinear devices. Some exemplary devices and techniques for addressing these needs are described in copending and commonly assigned U.S. patent application Ser. No. 11/149,511, entitled “Fiber-Coupled Single Photon Source” (Attorney Docket No. 200406613-1), filed Jun. 10, 2005, the disclosure of which hereby is incorporated by reference herein.

FIG. 1 illustrates an exploded view of a device according to an embodiment of the invention, comprising an exemplary nanoparticle 110 coupled to a waveguide 150 and a backreflector 130. Nanoparticle 110 is able to emit a photon on demand, and thus can serve as a photon source.

An exemplary nanoparticle 110 is a particle with dimensions smaller than the wavelength of light, that can be made to emit photons at a desired wavelength at which a device using an embodiment of the invention will operate. Typically, nanoparticle 110 is approximately 10-100 nm in diameter. Generally, for a nanoparticle 110 to be useful in a device according to an embodiment of the invention, the nanoparticle 110 must provide a single quantum system that can be addressed optically; or if there are multiple quantum systems, it must be possible to address them individually through frequency selection.

In some embodiments, the nanoparticle 110 is grown in a semiconductor substrate. Group IV, Group III-V, or Group II-VI semiconductor materials may be used. A typical material may comprise Si or GaAs.

An exemplary nanoparticle 110 can be joined to either the backreflector 130 or to the waveguide 150, or to both. For example, the nanoparticle 110 can be placed or grown on the backreflector 130, or can be placed or grown on the end of waveguide 150. Illustrative examples of a suitable nanoparticle 110 include nanocrystals such as a diamond nanocrystal with nitrogen vacancy (NV) center, and a semiconductor nanocrystal. In a further embodiment, nanoparticle 110 can comprise an electrically driven or optically driven quantum dot. Quantum dots are capable of generating a single photon when excited by an electrical charge or an optical laser. Further examples of nanoparticle 110 include a self-assembled quantum dot placed or grown on the backreflector 130 or in a micropillar on the backreflector 130.

In the illustrated embodiment, the waveguide 150 is photonic crystal fiber, which is capable of suppressing leaky modes. Photonic crystal fiber, referred to as “holey” fiber, comprises a plurality of airhole passages 160 residing within the fiber. Examples of suitable photonic crystal fiber may be either solid or hollow core. In other embodiments, the waveguide 150 can be a suitable hollow-core bandgap fiber capable of suppressing leaky modes, e.g., omniguide fiber.