Molecular qubits stick around for longer

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+  Researchers in China have shown that the spin of a molecular quantum bit (qubit) can remain coherent for more than 1 millisecond – long enough to perform 145 000 basic logic operations. This number, known as the qubit “figure of merit”, is 40 times higher than previously reported for this molecule, raising the chances that such qubits could be used in quantum computing applications as well as in biomedical imaging and quantum sensing.

The researchers, who report their work in Chinese Physics Letters, say they now plan to steer the spin coherence of their molecular qubit at the single molecular level. “This is a key step for a molecular qubit in quantum information processing and is very challenging because the signal from a single molecular qubit is very weak,” Rong says.


+  Like all qubits, however, the superposed states in molecular qubits are fragile and easily disrupted by noise in the environment. This noise destroys the quantum information stored in the states, in a process known as decoherence. While various methods exist for overcoming decoherence in molecular qubits (including diluting the qubits in a diamagnetic matrix, enhancing the rigidity of the molecules and isotropic purification), the longest coherence time measured for a molecular qubit to date has been less than a millisecond.

+  A team at the University of Science and Technology in Hefei has now improved on that figure by applying microwave pulses to “flip” the quantum state of molecular qubits – a method known as dynamical decoupling. As team member Xing Rong explains, inverting the state of the molecule’s electron spin greatly averages out the coupling, or interaction, between the qubit and its environment, so extending the qubit’s coherence time.

Source:  Physics World.  Isabelle Dumé,  Molecular qubits stick around for longer…

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