Optická kvantová hradla výrazně účinnější

Efficient construction of various quantum gates is a crucial prerequisite for practical quantum computing and communications. In our Letter (Phys. Rev. Lett. 114, 153602), we experimentally demonstrate how to implement an optimal controlled-unitary gate on individual photons using linear optics. This gate is particularly interesting since it is known to be a key component for quantum circuits design. It makes quantum state of a target photon evolve depending on the state of a control photon. On the platform of linear optics, where such gate can only be implemented probabilistically, our scheme maximizes the achievable success rate. Instead of using two controlled-NOT gates, we use only one controlled gate with tunable interaction strength between the photons. This way we can increase the success probability of the entire scheme by about an order of magnitude and this improvement increases exponentially with the size of a quantum circuit. This provides, quoting one referee of our Letter, a `drastic’ improvement. We also show that our scheme can readily be incorporated in larger quantum circuits which makes it a valuable element of optical quantum circuits design.