Quantum Simulation

While quantum computers are, in principle, extremely powerful than today's digital computers, noise and lack-of-scalability severely limits their true potential. Quantum simulation with with current generation quantum hardware requires customisation so that the use of noisy multiparty-gates can be minimised. Promising candidates in this direction are the so-called variational quantum algorithms. These consist of a classical optimiser together with a parametrised quantum circuit, and have been shown to be universal for quantum computation. In particular, quantum approximate optimisation algorithm (QAOA) have been proven to be an efficient tool to simulate many-body system. The canonical version of the protocol cannot be applied directly to any many-body systems especially for longer range systems since an exponentially large number of parameters need to be optimised over multiple iterations and therefore the simulation becomes inefficient. We look for ways to customise these protocols such that efficient simulation becomes reality.

Related Publications:
Lakkaraju, Ghosh, Sadhukhan and Sen(De), Mimicking quantum correlation of a long-range Hamiltonian by finite-range interactions, Phys. Rev. A 106, 052425 (2022)

Quantum Error Mitigation

Because of the hefty overhead cost of the quantum error correction, the era of the fault-tolerant quantum computation may still be rather distant and the best choice that we have today to push the current limits, at least for the currently available limited-size quantum hardwares, is probably quantum error mitigation where the overhead is not in the system size but in the sample size of the quantum data which is relatively easy to generate using the current generation of quantum architectures. We look for ways to suppress the error as much as possible playing around with the post-selection strategies and try to guess the noiseless expectation value of an observable without actively correcting the noisy quantum state. 

Related Publication:

Mills, Sadhukhan and Kashefi, Simplifying errors by symmetry and randomisation, arXiv:2303.02712 (2023)