Research

Quantum Error Correction

Img One of the central challenges in building a quantum computer is that the qubits do not maintain their quantum nature for a very long time. This phenomena is called decoherence and happens primarily due to environmental noise. However, it is possible to use multiple imperfect qubits to build a near-perfect qubit using a process called quantum error correction. This involves encoding the single qubit state among multiple physical qubits, making the right kind of measurements to detect any errors and then use feedback to correct those errors. We are investigating techniques to implement quantum error correction using weak continuous measurements and feedback.


Quantum Simulations

Img The computational resources required to simulate quantum mechanics on a classical computer grows exponentially with the size of the simulated system. Feynman had originally suggested that one should use quantum systems to simulate quantum mechanics. The basic idea is to have a well characterized and controllable quantum system to mimic the behaviour of other systems of interest. Our lab is interested in studying collective behaviour in superconducting qubits and developing the necessary architecture for performing quantum simulations.



Novel qubit designs

Img We are working on novel qubit designs where a single superconducting circuit can be used to implement a coupled multi-qubit system. We are exploring such multi-qubit systems for quantum error correction and quantum simulations.







Quantum limited parametric amplifiers

Img Parametric amplifiers have become an essential component of high fidelity quantum measurement setups. We are working on developing new amplifier designs which have enhanced bandwidth ( See paper here) and dynamic range to enable multiplexed multi-qubit measurements. Such amplifiers will also enable new experiments in microwave quantum optics.





Weak quantum measurements

Img We are exploring weak quantum measurements in superconducting circuit QED architecture for applications in quantum error correction, quantum feedback and quantum metrology.






Nanomechanical systems in the quantum regime

Img Recent advances in nano-fabrication techniques have enabled the fabrication of nano-mechanical oscillators capable of displaying quantum phenomena. We are working on combining such nano-mechanical oscillators with superconducting circuits to explore new regimes in quantum measurement.






Useful links

A review article on superconducting quantum bits : Link

A more recent review article on superconducting quantum bits : Link

Vijay's talk at Dartmouth College in 2012: Abstract ||Video

A classic reference for Quantum Computing and Quantum Information: Link

Useful Theses

One of the first thesis on superconducting qubits: Cottet's Thesis

Vijay's thesis on the Josephson Bifurcation Amplifier: Vijay's thesis

David Schuster's thesis on circuit quantum electrodynamics (cQED) architecture: Schuster's Thesis