Counterfactual Quantum Computation

---

"Counterfactual quantum computation" (CFC) refers to a protocol in which one performs a measurement on a quantum computer and obtains information about the solution to a problem without the computer actually running. Recently, we have demonstrated the first experimental realization of CFC [the Nature article, supplementary information]. In addition to theoretically demonstrating some error-suppressing capabilities of a non-running quantum computer, we proposed a scheme which showed an apparent breakdown of the previously established bounds on how good of a CFC one can achieve in principle. This initiated an ongoing debate on the meaning of counterfactuality in quantum processes, so far in three different approaches: history decomposition methods (and our response), quantum weak measurements (and our response), and 'consistent histories interpretation' of quantum mechanics.