A 'smooth gate' method is proposed for entangling qubits on trapped ions, in which residual spin-motion entanglement errors are adiabatically eliminated through linear detuning ramping. Two-qubit gates with electronic control were demonstrated, with an estimated error of 8.4(7)×10⁻⁵ without cooling to the ground state. The error stays at ≲5×10⁻⁴ for an average phonon mode occupation up to n̄ = 9.4(3). The results show that ion-based quantum computing can be performed with high fidelity at temperatures above the Doppler limit, simplifying and speeding up device operation.
A lone ion in a trap jitters like a swing, and each oscillation introduces an error into quantum calculations. Traditionally, jitter is suppressed by cooling almost to absolute zero—this is bulky and expensive.
Physicists have found an elegant solution: the laser pulse smoothly changes frequency right during operation, canceling jitter. The beam acts like a precise push that stops the swing: instead of fighting the shaking, it harnesses it, calming the system’s entropy (disorder). A final check is performed by a detector with photometry—measuring faint light—and the error drops to 0.0084%. Remarkably, even with a ninefold increase in jitter, failures don’t exceed 0.05%.
Thus, the ideas of David Wineland and the dreams of Richard Feynman for accessible quantum machines are becoming reality—without the icy hell.
🎯 The temperature to which ions are typically cooled for quantum computing is thousands of times lower than interstellar space—colder than almost anything in the Universe.