The Polyquantique research group led by Nicolás Quesada specializes in quantum photonics and quantum information. The group is looking for highly motivated candidates at all levels (graduate students, postdocs) with expertise or interest in quantum photonics, quantum information, quantum optics, quantum metrology, quantum error correction, topological photonics or machine learning.

About the group

We are a theory group with a significant computational component that collaborates closely with experimental groups and partners in government and industry. We write open source code and do reproducible science (that is, making all data and code available to others to easily execute).

We believe that a significant part of scientific research can be understood as collective problem solving. Not having a group that can look at problems from diverse vantage points is a wasted opportunity. We are thus committed to building a diverse research group from its conception and to being attentive to and supportive of the needs and ambitions of students and postdocs, especially those who belong to marginalized or underrepresented groups in science and engineering.

We are based in beautiful and welcoming Montréal, a safe but never boring city that consistently ranks as the best city in North America to be a student.

Our research

Quantum technologies offer the promise to solve practical problems in chemistry and material science with a level of precision and speed that is beyond the reach of any classical supercomputer. They also allow us to envision impregnable information networks for secure communication and provide us with the most precise and gentle probes to study delicate materials and biological samples.

Photonics is a strong contender for building these quantum technologies: unlike other physical substrates for quantum technologies, light does not decohere at room temperature, light qubits can be easily encoded in time bins, allowing for massive scalability, and there is already very significant industrial capacity built around it.

We investigate how to generate states of light in which quantum information can be encoded. The generation of these states requires nonlinear interactions between modes of light, which can be mediated by matter in the form of nonlinear materials or by measurements on parts of an entangled (quantum-correlated) state using photon counting detectors.

We use mathematical and computational tools, including inverse design, machine learning and tensor networks, to obtain optimal designs for structures, devices and protocols needed for the generation of these states and the operation of the detectors needed to measure them. These tools are not only useful for designing states for quantum computing, but also for generating states of light with metrological applications, such as squeezed light in which vacuum noise in a quadrature of the electromagnetic field is suppressed. At the same time, these quantum states can provide a viable route to build a network where quantum, instead of classical, information is exchanged: a quantum internet.

Potential Projects

Below we provide a list of possible projects. If you are a applying to be a graduate student , and you enjoyed your quantum mechanics, quantum optics, quantum information or photonics courses and liked the mathematical/computational aspects of these areas you will likely enjoy working with us in one of the projects below (a concrete project can be defined at a later stage).

1. Inverse design for pulsed squeezed light

Squeezed light is perhaps the easiest type of non-classical light that can be generated in a deterministic way. For many applications, especially when doing heralding experiments for the generation of bosonic states useful for error-correction, the squeezed light needs to be generated in a single consistent temporal mode. This implies that whenever photons are counted in a heralding setup no which-path information can damage interference. The aim of this project is to develop inverse-design methods for the optimization of squeezed light sources in resonators and waveguides in a single consistent temporal mode.

2. Optimal Heralding Protocols

With optimal sources of squeezed light at hand, the next step for the generation of bosonic code states, or any other non-Gaussian state, is to find optimal ways of interfering and measuring these states. The aim of this project is to develop methods for finding optimal interferometric schemes for non-Gaussian state generation, including realistic imperfections such as mode mismatch, loss, dark counts and photon number miscategorization. The methods used to tackle this problem will borrow many ideas from machine learning. For example, the interferometers will play the role of the linear part of a neural network, while the measurement acts like the nonlinear ‘activation function’. These schemes will ultimately lead to understanding the possibilities and limitations of nonlinear optical heralded sources for error-correction and their use in the context of quantum computation and communication.

3. Deterministic non-Gaussian light

A different approach to generate non-Gaussian light useful for error correction is to strongly drive material nonlinearities to the point where any linear approximation to study the dynamics of the quantized electromagnetic field breaks down. Multiple experimental teams are approaching this limit by carefully engineering nonlinear structures in a manifold of materials. At this stage, the theoretical treatment of the quantum states generated in these structures requires new tools beyond the ones used to deal with squeezed light. The aim of this project is to develop these new tools, which will likely involve a mix of Gaussian continuous-variable techniques, tensor network methods and statistical approximations such as cumulants expansions.

4. Boson Sampling benchmarking

One of the most appealing proposals to demonstrate quantum advantage, when a quantum processor performs calculations beyond the reach of any classical supercomputer, is Gaussian Boson Sampling. This quantum photonic architecture consists of squeezed light which is sent into an interferometer and is then measured using photon counters. Unlike for random circuit sampling, another leading approach to demonstrate quantum advantage, very little is known about how to certify the quantum advantage of a Gaussian Boson Sampler, and this is precisely the main goal of the project. We aim to answer the question: how can one certify that a Gaussian Boson Sampler is indeed performing a task beyond the capabilities of any classical supercomputer?

Interested in joining?

In order to start in the Fall of 2022, international graduate students applicants should send their applications by February 15 / 2022; Canadian citizens and permanent residents should send their application no later than March 15 / 2022. Invitation letters for graduate students will be sent in early April. Postdoc applications will be reviewed until filled.

Reach us by email (nicolas.quesada@polymtl.ca) with the subject: “[Name], Master/PhD/Postdoc Applicant” including the following information:

A motivation letter (2 pages max.) describing your research interests, background and experience.

A curriculum vitae.

For Master/PhD applicants, course transcripts, when available. These can be submitted in French, English, Spanish or Portuguese. For Postdoc applicants the names of two researchers familiar with the applicants work, and willing to provide a letter of reference.