ALP Seminar: Will (near-term) quantum computers deliver real advantage?

Quantum computers are becoming a reality and current generations of machines are already well beyond the 50-qubit frontier. However, hardware imperfections still overwhelm these devices and it is generally believed the fault-tolerant, error-corrected systems will not be within reach in the near term: a single logical qubit needs to be encoded into potentially thousands of physical qubits which is prohibitive. It is thus a very exciting challenge in the near term to achieve practical value with noisy intermediate-scale quantum (NISQ) devices. 

Due to limited resources, in the near term, we need to resort to quantum error mitigation techniques. I will explain the basic concepts and then discuss recent breakthrough results on exponentially effective error mitigation, including an architecture of multiple quantum processors that perform the same quantum computation in parallel; using their outputs to verify each other results in an exponential suppression of errors. In the second part of my talk, I will explain that the most promising candidates for achieving value in the NISQ era are variational quantum circuits. These have the potential to solve real-world problems---including optimisation or ground-state search---but their main drawback is they rely on a non-trivial optimisation (training).  I will explain a recent development that uses extremely powerful classical shadows to accelerate training in a way previously thought impossible. I will finally identify the most likely areas where quantum computers may deliver a true advantage in the near term. 

This talk will be based on the papers [PRX 11 (3), 031057, arXiv:2011.05942], [PRApplied, in production, arXiv:2201.08861], [PRX, in production, arXiv:2204.08494].