Research

Our group pursues multiple projects focused on the development of quantum communication devices and practical quantum memory buffers using light. The end goal is that these devices will serve as the components that will comprise the quantum networks of the not too distant future. These networks will be capable of many powerful applications including fully secure data encryption through quantum key distribution.

The field of quantum communications is presently at a stage of transition from a research field into an engineering discipline and bring force a demand personnel trained with a unique sill set. Hence, our lab is aldedicated to training and mentoring of students to enter the future quantum workforce. Projects will allow students to become trained and skilled tools and devices that they will encounter as future quantum communications engineers.

Robust Quantum Memory Systems for Real-World Deployment

Similar to a classical communication network, the transmission backbone of the quantum version will be based on photonics and light. The major elements necessary for a practical long-distance quantum network include i) a dependable source of light encoded with quantum information such as single photons, ii) a transmission channel compatible with the wavelengths of the source, iii) practical and well-understood detection techniques/schemes and iv) a robust optical quantum memory device with suficient operating characteristics. While these facets individually require a significant amount of attention, they will ultimately need to “speak to” one another and smoothly integrate into telecommunication systems for a real-world quantum network to be realized.

The last element listed, an optical quantum memory (QM) presents quite a challenge. Such a device is crucial to transmit quantum light over trans-continental distances and serves as the quantum analog to classical amplifiers used in undersea optical fibres to regenerate classical signals at intermediate stages. Any optical QM device needs to capture, hold and release light states/photons on demand, all while preserving the quantum nature of the light states. In other words, a QM must indiscriminately receive an arbitrary quantum state without ever knowing what it is but, ideally, would know that `some state’ is present. In the immediate future QM devices will have major implications for extending real-world QKD through a technique called measurement device independent QKD and quantum teleportation. However a system proven capable of wide-scale deployment remains elusive.

A promising optical QM candidate are atomic ensembles, typically the alkali metals of rubidium or cesium. The storage occurs by conditioning the resonances of these elements to map the excitations of a weak electromagnetic field to the collective nature of atoms in a coherent and reversible fashion. This often requires additional control laser fields that mediate the storage and retrieval operations. Of the first techniques shown capable of this operation was a quantum interference effect known as electromagnetically induced transparency (EIT). This coherent, nonlinear effect allows one to modulate the refractive index and slowdown light pulses near atomic resonance to the point of stopping them.

EIT has shown viable for storing single and entangled photons. Atomic ensemble-based systems can be optimized for different metrics depending on the application. Warm vapour systems hold a distinct advantage in terms of practicality, a vapour cell system operates in a controlled environment near room temperature. The simplistic, low overhead implementation in combination with their proven QM operation make vapour cells ideal candidates for wide-scale deployment.

The remaining key piece is the engineering of these QM systems to a modular form that would be suitable for wide-scale deployment to numerous nodes of a quantum network. This task is presently being pursued by my collaborators at Qunnect (Brooklyn, NY).

High bandwidth quantum protocols using commercial components

Data encryption and transmission with security verified by quantum mechanical laws would have implications spanning many sectors including financial banking, national defence, online commerce and data privacy. For this unconditional security to become a reality, a specialized encryption key verified by quantum statistics must be shared between two separated but trusted parties (or i.e. ends of a transmission line) and is commonly known as quantum key distribution QKD. The versatility and degrees of freedom characteristic of light has led to numerous successful QKD implementations.

When QKD schemes are transitioned to real-world networks they will need to smoothly and successfully integrate with metropolitan fibre systems. Our group aims to develop and test quantum communication schemes that interface state-of-the-art telecommunication devices with quantum state measurement techniques. Specifically, commercial phase amplitude modulations have the ideal functionality for continuous variable QKD (CVQKD) encoding. This QKD method uses data encoding based on localizing electric field fluctuations to specific phase and amplitude values. The field of a quantum state can be measured using a balanced homodyne detection (BHD) technique which processes data characterizes the quantum state in the same phase space used for telecommunications encoding.

New species of quantum photonic devices based on silicon nitride

The bandwidth of QKD can be increased by utilizing multiple photonic degrees of freedom (DOF) just as the telecommunications industry does (i.e. greater DOF translates to higher information capacity). Photonic disk resonators fabricated from silicon nitride (Si3N4) are superb candidates for this DOF requirement. These `microdisks’ exhibit numerous of distinguishable yet coherent, frequency bands (frequency comb) where every band can contain multiple bits of data. The frequency spectrum exhibited by Si3N4 can be tailored to telecommunication wavelengths for compatibility with industry devices such as wavelength division multiplexers for data processing.