Physicists merge two photons into one

Gary Taubes

The word laser has taken on a new meaning: a beam of atoms marching in quantum lockstep, like the photons of a light laser. Two years ago, physicists achieved the crucial starting point for an atom laser, which could aid everything from atomic clocks to chipmaking, when they created an exotic brew of atoms all merged in a single quantum state. Now, a group at the Massachusetts Institute of Technology reports in this issue ( p. 637 ) that they have shaped this “Bose-Einstein condensate” into pulses, each one a single, coherent “matter wave.”

Chiara Vitelli, Nicolò Spagnolo, Lorenzo Aparo +3 more

Hai‐Rui Wei, Gui Lu Long

We propose two compact, economic, and scalable schemes for implementing optical controlled-phase-flip and controlled-controlled-phase-flip gates by using the input-output process of a single-sided cavity strongly coupled to a single nitrogen-vacancy-center defect in diamond. Additional photonic qubits, necessary for procedures based on the parity-check measurement or controlled-path and merging gates, are not employed in our schemes. In the controlled-path gate, the paths of the target photon are conditionally controlled by the control photon, and these two paths can be merged back into one by using a merging gate. Only one half-wave plate is employed in our scheme for the controlled-phase-flip gate. Compared with the conventional synthesis procedures for constructing a controlled-controlled-phase-flip gate, the cost of which is two controlled-path gates and two merging gates, or six controlled-not gates, our scheme is more compact and simpler. Our schemes could be performed with a high fidelity and high efficiency with current achievable experimental techniques.

Philippe Grangier

Adrian Cho

QUANTUM PHYSICSFulfilling a decades-old prediction, physicists have spotted the merging of several tiny whirlpools of current in a superconductor into a single giant vortex.