Projects
Next Generation APDs
The primary objective of the group’s APD team is to design and fabricate next generation quantum photon sensors. Tapered nanowires offer unique absorption characteristics, namely in their anti-reflection and near unity broadband absorption, as seen in finite difference time domain simulations (figure (a)). Combining these attributes with a p-n junction doping profile enables APD behaviour capable of single photon distinguishability. Preliminary measurements of an InP APD device (figure (b)) have already been performed to demonstrate high speed, high gain, broadband, single photon distinguishability in the visible region at room temperature. The current efforts of the team are focused on developing InGaAs devices (figures (c) and (d)) in the interest of extending functionality into the near-infrared regime for application in modern telecom technologies. By omitting the need for cryogenic cooling, these devices offer a promising technology for single photon detection applications for the first time.
On-demand Nanowire Quantum Dot Entangled Photon Sources
Entangled photon sources are crucial for quantum optics, quantum sensing, and quantum communication. Semiconductor quantum dots in nanowires have recently emerged as leading candidates to generate entangled photons due to their high brightness and directional Gaussian emission profile for near-unity fiber coupling. However, the structural asymmetry of the quantum dot lifts the degeneracy of the intermediate exciton states in the cascade, thus limiting the use of quantum dots (QDs) as a source of entangled photon pairs with high fidelity. This energy separation is known as fine-structure splitting (FSS). In our group, we are working on two different approaches to address this challenge. The first is by fabricating nanoscale metal gates around the plane of the quantum dot and applying a quadrupole electric field (figure 1). We have shown that by applying a quadrupole field, the spatial asymmetry of the excitonic wave function can be tuned without compromising the spatial overlap (QD brightness) between electrons and holes. A second approach is an all-optical approach (figure 2) using rotating waveplates to erase this fine-structure splitting. This bears the advantage that the fine-structure splitting of quantum dots in nanowires and micropillars can be directly compensated without the need for further sample processing.
Hybrid Quantum Repeater based on Atomic Quantum Memories and Telecom Wavelength Entangled Photon Pairs Generated from Semiconductor Nanowire
Losses in physical channels, such as optical fibers, limit existing quantum communication systems to modest distance ranges. Since amplification of quantum signals is fundamentally not possible, we look to extend the range and functionality of these quantum channels by adding quantum memory nodes that can daisy-chain multiple lengths of quantum channels through entanglement and thus extend the communication distance — an approach known as ‘quantum repeater’. Quantum repeaters are by necessity hybrid devices, as they connect flying qubits (photons) to small processors for error correction and privacy amplification. In this project we develop a two-node proof-of-principle hybrid quantum repeater system. We generate entangled photon pairs from quantum dots embedded in semiconductor nanowires and store them in atomic quantum memories following a frequency up-conversion. We expect this will enable quantum key distribution over long distances at rates exceeding those possible through a direct link. The photon-pair sources, the frequency converters, as well as the quantum memories will be implemented in compact on-chip platforms. This novel approach combines the advantages available from a deterministic and tunable solid-state source of bright entangled photon pairs with the potential for high-efficiency long-lived quantum memory that is achievable with laser cooled atoms. The ultimate goal is to achieve a working pair of quantum repeater nodes at practically relevant wavelengths that would lead to useful rates for long-distance quantum key distribution.
This project is a collaboration between the Quantum Photonic Devices lab (PI: Dr. Michael Reimer) and the Nano-photonics and Quantum Optics lab (PI: Dr. Michal Bajcsy), and, is funded by Transformative Quantum Technologies (TQT).
This project is a collaboration between the Quantum Photonic Devices lab (PI: Dr. Michael Reimer) and the Nano-photonics and Quantum Optics lab (PI: Dr. Michal Bajcsy), and, is funded by Transformative Quantum Technologies (TQT).
All-electric High Frequency Quantum Emitters based on III-V Semiconductor Heterostructure Material
The strong quantum correlations that exist between two entangled photons can be used to enhance target detection and sensing in noisy environments, in a paradigm called quantum illumination. The development of on-demand, high frequency quantum emitters is key to the realization of practical technologies based on quantum illumination. Undoped III-V semiconductor heterostructure materials grown using Molecular Beam Epitaxy (MBE) possess few impurities and thus high charge carrier mobilities. By simultaneously inducing separate two-dimensional charge gases of opposite polarities (at either a single heterojunction interface or within a quantum well) in this heterostructure wafer stack, we create a 2D p-n junction. Adding a means of shuttling charges one at a time across the junction at a high frequency (for example by using a single electron pump) results in electron-hole recombination and single photon emission at a high frequency. Further, shuttling two charges at a time results in the simultaneous emission of two correlated or entangled photons. Such a technology can prove useful in applications such as biological sensing, secure communication and long-range imaging and detection.
This project is a collaboration between the QPD group, the Coherent Spintronics group (PI: Prof. Jonathan Baugh) and the Molecular Beam Epitaxy research group (PI: Prof. Zbig Wasilewski).
This project is a collaboration between the QPD group, the Coherent Spintronics group (PI: Prof. Jonathan Baugh) and the Molecular Beam Epitaxy research group (PI: Prof. Zbig Wasilewski).
Photonic Integrated Circuits
The ability to generate ‘ideal’ entangled photon pairs for applications in quantum photonic technology will impact society by ensuring the security of communication and enhancing computation to solve certain problems that are not possible with present day computers. To realize enhanced computation, thousands of photons must be coherently controlled and manipulated. Such a formidable task is not practical on an optical bench in a laboratory setting (bulk-optics), but when scaled down to photonic integrated circuits (PICs) at a chip level in a well-established foundry process this becomes possible. However, most of the quantum optics experiments performed with PICs to manipulate photons have utilized probabilistic sources of single and entangled photons, which have limited efficiency as compared to sources based on semiconductor quantum dots in photonic nanostructures. For this reason, we are working on integrating semiconductor quantum dots with PICs. Realizing such hybrid quantum photonic platforms is a technical challenge, but it is necessary for realizing large-scale quantum networks and photonic quantum computing. Our efforts will demonstrate that PICs provide superior performance to a bulk-optics implementation and show the benefits of quantum dot sources over spontaneous parametric down-conversion sources in terms of scalability and efficiency.