Strong algorithmic cooling in large star-topology quantum registers
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Abstract
We envisage a star-topology quantum register, wherein a central computation qubit is symmetrically surrounded by a set of reset qubits. The reset qubits cool the computation qubit by transferring its entropy to a heat bath with the help of a heat-bath algorithmic cooling (HBAC) procedure. By combining standard NMR methods with powerful quantum control techniques, we demonstrate HBAC on two large star-topology systems, with 13 and 37 spins respectively. We obtain polarization enhancements by a factor of over 24, and an associated reduction in the spin temperature from 298.0 K down to 12.4 K. Exploiting the enhanced polarization of computation qubit, we prepare combination quantum coherences of order up to 15. By benchmarking the decay of these coherences we investigate the underlying noise process. Further, we carry out HBAC of a pair of computation qubits and use the cooled qubits to prepare an effective pure-state.