# Strong Algorithmic Cooling in Large Star-Topology Quantum Registers

## TL;DR

This paper demonstrates a novel star-topology quantum cooling method that significantly enhances qubit polarization, enabling improved initialization for quantum computing using combined NMR and quantum control techniques.

## Contribution

It introduces a star-topology cooling scheme that achieves large polarization enhancements and effective pure-state preparation in multi-qubit systems.

## Key findings

- Polarization increased by over 24 times
- Reduced spin temperature from 298 K to 12 K
- Prepared high-order coherences up to 15

## Abstract

Cooling the qubit into a pure initial state is crucial for realizing fault-tolerant quantum information processing. Here we envisage a star-topology arrangement of reset and computation qubits for this purpose. The reset qubits cool or purify the computation qubit by transferring its entropy to a heat-bath with the help of a heat-bath algorithmic cooling procedure. By combining standard NMR methods with powerful quantum control techniques, we cool central qubits of 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 K down to 12 K. Exploiting the enhanced polarization of computation qubit, we prepare combination-coherences of orders up to 15. By benchmarking the decay of these coherences we investigate the underlying noise process. Further, we also cool a pair of computation qubits and subsequently prepare them in an effective pure-state.