What we do?

Quantum neural networks: Machine learning, Reservoir computing

Quantum reservoir processing is a quantum generalization of reservoir computing that is a form of artificial neural network. It is a universal architecture that can efficiently perform qualitative tasks like recognising entangled states or quantitative tasks like estimating von Neumann entropy, purity or negativity. While this architecture can be used as a software, it is specifically suitable for hardware implementation. Generically, it consists of a network of quantum objects (e.g. qubit) that is used as the computing unit for quantum information processing. This network can be realized in a variety of systems, e.g., arrays of semiconductor quantum dots, superconducting qubits, exciton polaritons in semiconducting microcavities, trapped ions and atoms, and NV centres in diamond. 

Quantum computing and information processing

We explore different systems for realizing quantum computing. Recently, we have proposed exciton polariton condensates as suitable platform for quantum computing. Exciton-polariton condensates have attractive features for quantum computation, e.g., room temperature operation, high dynamical speed, ease of probe, and existing fabrication techniques. Here, we present a complete theoretical scheme of quantum computing with exciton-polariton condensates formed in semiconductor micropillars. Quantum fluctuations on top of the condensates are shown to realize qubits, which are externally controllable by applied laser pulses. Quantum tunneling and nonlinear interactions between the condensates allow SWAP, square-root-SWAP and controlled-NOT gate operations between the qubits.

Quantum optics: Single photons

Single photon source is a quantum device that emits one photon at a time. These devices are essential component for many emerging quantum technologies, such as quantum computing, quantum communications and quantum cryptography. A perfect single photon source has a zero g_2 correlation function that signifies no multi-photon emission. The phenomenon that shows g_2=0 is known as antibunching and can be induced by photon blockade. Analogous to Coulomb blockade, the prevention of multi-photon occupation in a quantum mode due to interaction is known as the photon blockade.   

We have recently proposed a model of a single photon source that can be operated by incoherent excitations. 

Bosonic condensates: Light-matter interaction

Single photon source is a quantum device that emits one photon at a time. These devices are essential component for many emerging quantum technologies, such as quantum computing, quantum communications and quantum cryptography. A perfect single photon source has a zero g_2 correlation function that signifies no multi-photon emission. The phenomenon that shows g_2=0 is known as antibunching and can be induced by photon blockade. Analogous to Coulomb blockade, the prevention of multi-photon occupation in a quantum mode due to interaction is known as the photon blockade.   

We have recently proposed a model of a single photon source that can be operated by incoherent excitations. 

Disordered systems: Anderson localization, Metal-insulator transition

I am interested in disordered quantum systems. In particular, I study the transport properties of ultra-cold atoms subjected to random potentials induced by laser speckles. An intriguing phenomenon known as Anderson localization occurs in disordered systems due to strong multiple phase-coherent scattering. The natural way to study such phenomena is to look at the spreading of an initial narrow wave packet. The absence of wave packet expansion indicates Anderson localization. However, such observations do not distinguish between the Anderson localization and various incoherent effects, such as, absorptions, classical trapping etc. 

Momentum signatures: We instead, look into the momentum space, and study the properties of the coherent backscattering (CBS) and recently introduced coherent forward scattering (CFS) peaks. We have shown that, it is possible to fully characterize Anderson localization/transition by observing these coherent peaks in momentum space. These peaks do distinguish between coherent and incoherent processes.

Superconductivity

The effect of disorder in superconductivity is another interesting topic for exploration. It has been shown that disorder can induce various intriguing phenomena in superconductivity, e.g., superconductor-insulator transition, rapid amplitude and phase fluctuations. They can be used for practical applications.