Neutral atom quantum computing : Quantum gates and Maxwell's demon

Aishwarya Kumar, Tsung-Yao Wu, Yang Wang +1 more

Chuck Easttom

M. Koch, Christian Sames, Alexander Kubanek +8 more

Maxwell realized in a famous thought experiment, which is nowadays known as Maxwell's demon, that the thermodynamic parameters of a system can be altered by performing feedback on the system's individual constituents. Here we report on the implementation of a related scheme to cool the motion of a single neutral atom.

A. V. Lebedev, Gordey B. Lesovik, V. M. Vinokur +1 more

A quantum Maxwell demon is a device that can lower the entropy of a quantum system by providing it with purity. The functionality of such a quantum demon is rooted in a quantum-mechanical SWAP operation exchanging mixed and pure states. We describe the setup and performance of a quantum Maxwell demon that purifies an energy-isolated system from a distance. Our cQED-based design involves two transmon qubits, where the mixed-state target qubit is purified by a pure-state demon qubit connected via an off-resonant transmission line; this configuration naturally generates an iSWAP gate. Although less powerful than a full SWAP gate, we show that assuming the present-day performance characteristics of a cQED implementation, such an extended quantum Maxwell demon can purify the target qubit over macroscopic distances on the order of meters and tolerates elevated temperatures of the order of a few Kelvin in the transmission line.

W.-B. Wang, X.-Y. Chang, F. Wang +9 more

We report experimental realization of a quantum version of Maxwell's demon using solid state spins where the information acquiring and feedback operations by the demon are achieved through conditional quantum gates. A unique feature of this implementation is that the demon can start in a quantum superposition state or in an entangled state with an ancilla observer. Through quantum state tomography, we measure the entropy in the system, demon, and the ancilla, showing the influence of coherence and entanglement on the result. A quantum implementation of Maxwell's demon adds more controllability to this paradoxical thermal machine and may find applications in quantum thermodynamics involving microscopic systems.