Abstract
Physical implementation of quantum gates acting on qubits does not achieve a perfect fidelity of 1. The actual output qubit may not match the targeted output of the desired gate. According to theoretical estimates, intrinsic gate fidelities >99.99% are necessary so that error correction codes can be used to achieve perfect fidelity. Here we test what fidelity can be accomplished for a CNOT gate executed by a shaped ultrafast laser pulse interacting with vibrational states of the molecule SCCl2. This molecule has been used as a test system for low-fidelity calculations before. To make our test more stringent, we include vibrational levels that do not encode the desired qubits but are close enough in energy to interfere with population transfer by the laser pulse. We use two complementary approaches: optimal control theory determines what the best possible pulse can do; a more constrained physical model calculates what an experiment likely can do. Optimal control theory finds pulses with fidelity >0.9999, in excess of the quantum error correction threshold with 8 × 104 iterations. On the other hand, the physical model achieves only 0.9992 after 8 × 104 iterations. Both calculations converge as an inverse power law toward unit fidelity after >102 iterations/generations. In principle, the fidelities necessary for quantum error correction are reachable with qubits encoded by molecular vibrations. In practice, it will be challenging with current laboratory instrumentation because of slow convergence past fidelities of 0.99.
Original language | English (US) |
---|---|
Pages (from-to) | 11347-11354 |
Number of pages | 8 |
Journal | Journal of Physical Chemistry A |
Volume | 116 |
Issue number | 46 |
DOIs | |
State | Published - Nov 26 2012 |
ASJC Scopus subject areas
- Physical and Theoretical Chemistry