Quantum computing with composite pulses and coherent population trapping

S. Stortini, Irene Marzoli

Ingela Roos, Klaus Mølmer

Gate operation schemes are presented for quantum computing with rare-earth-ion qubits in inorganic crystals. The inhomogeneous broadening of optical transitions in the ions is used to address individual qubits, but the transition frequencies do not need to be precisely specified for the gates to have high fidelity.

J. I. Cirac, Thomas Pellizzari, J. F. Poyatos +1 more

Ingela Roos, Klaus Mølmer

The proposal for quantum computing with rare-earth-metal-ion qubits in inorganic crystals makes use of the inhomogeneous broadening of optical transitions in the ions to associate individual qubits with ions responding to radiation in selected frequency channels. We show that a class of Gaussian composite pulses and complex sech pulses provide accurate qubit $\ensuremath{\pi}$ rotations, which are at the same time channel selective on a 5 MHz frequency scale and tolerant to $\ifmmode\pm\else\textpm\fi{}0.5\mathrm{MHz}$ deviations of the transition frequency of ions within a single channel. Rotations in qubit space of arbitrary angles and phases are produced by sequences of $\ensuremath{\pi}$ pulses between the excited state of the ions and coherent superpositions of the qubit states.

G. Demeter

We derive composite pulse sequences that achieve high-fidelity excitation of two-state systems in an optically dense, inhomogeneously broadened ensemble. The composite pulses are resistant to distortions due to the backaction of the medium they propagate in and are able to create high-fidelity inversion to optical depths $\ensuremath{\alpha}z>10$. They function well with smooth pulse shapes used for coherent control of optical atomic transitions in quantum computation and communication. They are an intermediary solution between single $\ensuremath{\pi}$-pulse excitation schemes and adiabatic passage schemes, being far more error tolerant than the former but still considerably faster than the latter.

Dipankar Bhattacharyya, Jyotirmoy Guha