A quantum computer uses the properties of superposition and interference to solve problems that are impossible with the computers and smartphones of today. However, building a quantum computer is an enormous physical and engineering challenge. In building a quantum computer, the first thing one needs to decide on is which quantum system, or “qubit”, is it going to use?
In Prof. Rajibul Islam’s group in the Department of Physics and Astronomy and the Institute for Quantum Computing, the qubit of choice are ions, or charged atoms. Ions are nature’s perfect qubit in many respects as all ions of the same atomic isotope are identical and they can be controlled using electric fields and laser light. They do however present experimental challenges related to the complex internal energy level structure of atoms and their strong coupling to electromagnetic fields.
Rajibul earned his BSc at Jadavpur University and MSc at the Tata Institute of Fundamental Research, both in India. He then wnet on to earn his PhD at the University of Maryland working with Chris Monroe and held a postdoctoral position at Harvard University with Markus Griener and another postdoctoral position with Vladan Vuletic at MIT. He joined the University of Waterloo in 2016 as an Assistant Professor of Physics and established the Laboratory for Quantum Information with Trapped Ions (QITI). Rajibul has hired a team of talented postdocs, research assistants, graduate and undergraduate students (from the physics and engineering programs) who have built up the QITI lab from an empty room to a new research powerhouse.
Rajibul’s lab is broadly focused on quantum computing and quantum simulation. Quantum computers have been shown theoretically to factor numbers, which is an important part of cryptographic protocols, and search databases faster than the best known classical algorithms. Quantum simulation uses one quantum system with excellent control to mimic the physics of another quantum system of interest, such as a quantum material or a biologically important molecule. By gaining a deeper understanding of such controlled ‘quantum simulators’, researchers hope to one day discover ways to make new materials that may have a big impact on our daily lives.
Rajibul’s quantum simulator is up and running. It uses a string of laser-cooled Ytterbium ions, electrically trapped inside an ultrahigh vacuum system. The ions have a temperature measured to be just a few microkelvin—a few millionths of a degree above absolute zero of -273.15 Celsius—and are held at ultra-low pressure, just a trillionth that of atmospheric pressure. They are working to scale up the number of ions they can control, which increases the complexity of the quantum system they can simulate and the computational power of their system.
The group has recently demonstrated that their system has the unique ability to measure a single qubit with laser light without affecting any of the others in the system, even when the others are as close as just a few micrometers away. This ability gives them a distinct advantage in the ion quantum computing and simulation field. For example, they can use the system for quantum error correction, coherently fixing errors and enabling longer computations. It also enables the study of exotic quantum material phenomena such as measurement driven quantum phase transitions.
It is an exciting time in experimental quantum computing and simulation thanks to developments in controlling larger and larger numbers of quantum systems. Ion trap quantum computing is one of the most promising platforms in this field and the work at the University of Waterloo conducted by Rajibul and his colleagues is leading the way.
