# Uncovering the mystery of the quantum world

The intriguing behaviour of particles at the quantum level promises computational power that surpasses any current computers we have seen in the modern world, and has the potential to revolutionise computing.

In an ordinary computer, information is processed in bits of 0 and 1. In quantum computing, the quantum bits, qubits, not only exist as discrete states of either 0 or 1, but several states at once. In theory, the qubits are also entangled so that the outcome of one qubit can tell us what we might expect from another qubit. This explains why the computational capacity of a quantum computer is exponentially higher than that of an ordinary computer.

Dr Ching-Kit Chan (Croucher Fellowship 2012) is a theoretical physicist at UCLA who is working on quantum physics including quantum computing and condensed matter physics.

“Despite the promises of quantum computing, quantum entanglements are extremely unstable, and will decay within a fraction of second – a phenomenon known as quantum decoherence,” said Chan. “This is one of the major challenges faced when attempting to put quantum computing to practical uses.”

Chan’s focus has been to understand the theory and mechanisms of quantum decoherence from first principles, to identify the main sources of error as a result of interactions between the qubit and the surrounding environment.

His task is to develop a theory to evaluate the decoherence and quantum noise of an open quantum system that can match the high fidelity requirement by the fault tolerant quantum computation. By using a diagrammatic technique similar to the Keldysh non-equilibrium Green’s function, Chan has successfully developed a way to precisely calculate quantum noise, and start to understand how fundamental quantum correlations between quantum control and quantum environment can arise.

In addition to providing insights into the principles of quantum decoherence, the techniques Chan developed also allow designs of quantum operations between different qubit systems. He and his colleagues have engineered a new protocol to entangle two qubits at a distance by projection measurements of their environments, leading to substantial improvements on the probability of success and the rate of entanglement as compared to existing single photon entanglement approaches.

After finishing his doctoral studies at the University of California San Diego and as a postdoctoral fellow at Harvard University, Chan moved to UCLA where he started an ambitious programme of research at the interface of condensed matter physics and optics. He works on topological materials, non-equilibrium phenomena, quantum phase transitions, many body physics and quantum information, and is working towards the implementation of novel quantum technologies.

“By using a combination of analytical and computational techniques, I hope to develop new topological materials with unconventional electrical and optical properties,” said Chan.

*Dr Ching-Kit Chan received his undergraduate degree and masters in Physics at the Hong Kong University of Science and Technology in 2005 and 2007, respectively, and PhD in Physics at University of California San Diego in 2012. Before joining The University of California at Los Angeles as an Assistant Adjunct Professor, he was a postdoctoral fellow at ITAMP, Harvard University, and a postdoctoral associate at Massachusetts Institute of Technology.*

To view Dr Chan’s Croucher profile, please click here.