Quantum repeaters based on individual electron spins and nuclear-spin-ensemble memories in quantum dots

Abstract

Inspired by recent developments in the control and manipulation of quantum dot nuclear spins, which allow for the transfer of an electron spin state to the surrounding nuclear-spin ensemble for storage, we propose a quantum repeater scheme that combines individual quantum dot electron spins and nuclear-spin ensembles, which serve as spin-photon interfaces and quantum memories respectively. We consider the use of low-strain quantum dots embedded in high-cooperativity optical microcavities. Quantum dot nuclear-spin ensembles allow for the long-term storage of entangled states, and heralded entanglement swapping is performed using cavity-assisted gates. We highlight the advances in quantum dot technologies required to realize our quantum repeater scheme which promises the establishment of high-fidelity entanglement over long distances with a distribution rate exceeding that of the direct transmission of photons.

Improved analytical bounds on delivery times of long-distance entanglement

“…The 3-over-2 approximation was first used by Jiang et al [39], who mentioned that the factor 3/2 agreed well with simulations in the small-probability regime. Since then, the approximation has been frequently used [8,10,28,32,[40][41][42][43][44][45][46][47][48][49][50][51][52].…”

“…For this scheme, it was empirically known [39] that for small success probabilities of connecting the pairs, the average time to in-parallel create both required initial pairs at each nesting level is roughly 3/2 times the average time for a single pair. This results in an approximation to the average completion time of the repeater scheme which is known as the 3-over-2 formula and has been frequently used since [8,10,28,32,[39][40][41][42][43][44][45][46][47][48][49][50][51][52]. Analytically finding the exact factor, for an arbitrary number of nesting levels and for any value of the success probabilities, has been an open problem for more than ten years [28].…”

Hybrid Quantum Repeaters with Ensemble-based Quantum Memories and Single-spin Photon Transducers

“…Different quantum hardware such as solid-state defect centers [5,6], atomic ensembles [7][8][9], trapped ions [10,11] and quantum dots [12] are currently being developed to enable a functional quantum repeater. There exist numerous theoretical proposals for repeater architectures tailored to the specific features of each hardware [13][14][15][16].…”