Final Report Summary - COOPAIRENT (Cooper pairs as a source of entanglement)
Quantum mechanics is known to describe the properties of nano-world, objects like atoms or molecules. Superconductors make an exception where the quantum state extends over the entire macroscopic piece of superconductor. This special macroscopic quantum state builds up from Cooper-pairs. Cooper-pair is a pair of electrons, which despite their repulsive Coulomb-interaction attract each other in a superconductor. This pairing is essential for the zero resistance of a superconductor, furthermore it also generates a key resource of quantum mechanics, the so-called quantum entanglement, which is a mian ingredient of quantum communicational or computational concepts.
In this project we focused on the development of nanocircuits which could separate the two electrons of a Cooper-pair. Although the two electrons get spatially separated they still remain quantum mechanically one object due to their spin entanglement. The so-called Cooper-pair Splitter (CPS) devices is a superconducting hybrid nanocircuit, which contains two quantum dots on the two sides of the superconductor.
As a first step we have investigated the required building blocks of CPS in different experimental platforms. We developed and studied various nanofabrication techniques to improve the performance of a CPS circuit (like etching of nanowires or suspending graphene). We introduced novel confinement potential for quantum dots either in semiconducting nanowires or in graphene platform. To develop analyzer circuits we produced well conducting quantized channels in graphene or investigated spin-orbit interaction in nanowires.
The new generation of CPS devices allowed to study the pair splitting in wide parameter range. Due to the tuneability of the circuits the pair splitting efficiency was explored as a function of tunnel coupling strengths, magnetic field or in out-of-equilibrium conditions as well. Based on our experimental findings we set up realistic minimal models of the CPS device and determined the efficient operational conditions. We managed to improve the efficiency of pair splitting by order of magnitude.
The original detection schemes of the entanglement of the split pairs seemed too challenging therefore we developed several new concepts to improve them. E.g. an improved spin sensitive detector can be achieved by replacing the tunnel interface of a ferromagnetic lead by a quantum dot, or entanglement detection can be performed by well controlled spin-qubit manipulation sequences.
Besides testing the fundamental quantum mechanical properties of electrons, an efficient generation of spin entangled electron pairs could find application in future spin qubit based architectures. Furthermore very recent concepts for topological quantum computing (like proposals for parafermions) also relies on splitting of Cooper pairs into two separated mediums, thus our detailed investigation of pair splitting will support the advancement of the field of topological superconductivity as well.
In this project we focused on the development of nanocircuits which could separate the two electrons of a Cooper-pair. Although the two electrons get spatially separated they still remain quantum mechanically one object due to their spin entanglement. The so-called Cooper-pair Splitter (CPS) devices is a superconducting hybrid nanocircuit, which contains two quantum dots on the two sides of the superconductor.
As a first step we have investigated the required building blocks of CPS in different experimental platforms. We developed and studied various nanofabrication techniques to improve the performance of a CPS circuit (like etching of nanowires or suspending graphene). We introduced novel confinement potential for quantum dots either in semiconducting nanowires or in graphene platform. To develop analyzer circuits we produced well conducting quantized channels in graphene or investigated spin-orbit interaction in nanowires.
The new generation of CPS devices allowed to study the pair splitting in wide parameter range. Due to the tuneability of the circuits the pair splitting efficiency was explored as a function of tunnel coupling strengths, magnetic field or in out-of-equilibrium conditions as well. Based on our experimental findings we set up realistic minimal models of the CPS device and determined the efficient operational conditions. We managed to improve the efficiency of pair splitting by order of magnitude.
The original detection schemes of the entanglement of the split pairs seemed too challenging therefore we developed several new concepts to improve them. E.g. an improved spin sensitive detector can be achieved by replacing the tunnel interface of a ferromagnetic lead by a quantum dot, or entanglement detection can be performed by well controlled spin-qubit manipulation sequences.
Besides testing the fundamental quantum mechanical properties of electrons, an efficient generation of spin entangled electron pairs could find application in future spin qubit based architectures. Furthermore very recent concepts for topological quantum computing (like proposals for parafermions) also relies on splitting of Cooper pairs into two separated mediums, thus our detailed investigation of pair splitting will support the advancement of the field of topological superconductivity as well.