Resource requirements for efficient quantum communication using all-photonic graph states generated from a few matter qubits

Abstract

Quantum communication technologies show great promise for applications ranging from the secure transmission of secret messages to distributed quantum computing. Due to fiber losses, long-distance quantum communication requires the use of quantum repeaters, for which there exist quantum memory-based schemes and all-photonic schemes. While all-photonic approaches based on graph states generated from linear optics avoid coherence time issues associated with memories, they outperform repeater-less protocols only at the expense of a prohibitively large overhead in resources. Here, we consider using matter qubits to produce the photonic graph states and analyze in detail the trade-off between resources and performance, as characterized by the achievable secret key rate per matter qubit. We show that fast two-qubit entangling gates between matter qubits and high photon collection and detection efficiencies are the main ingredients needed for the all-photonic protocol to outperform both repeater-less and memory-based schemes.

Photonic resource state generation from a minimal number of quantum emitters

“…Given that arbitrary graph states can be generated solely with Clifford gates 41,42 , which were also exclusively used in the protocols of refs. 24,25,[27][28][29][30][31]36 , restricting ourselves to this set does not affect the generality of our approach. Clifford gates enable the use of the stabilizer formalism, such that we can manipulate Pauli operators instead of keeping track of the whole state.…”

“…References 27,28 put forward protocols for 2D lattice graphs that leverage the principle that entangled emitters can emit entangled photons. This idea was extended further to develop protocols that deterministically generate resource states for quantum repeaters [29][30][31][32] -tailored to color centers in refs. 33,34 -and one-way computing 35,36 .…”

“…This is extremely resource-intensive, especially in light of the schemes for generating repeater graph states presented in refs. 29,31 , which require only two emitters regardless of the number of photons. The required resources (number of emitters and entangling gates) is a critical factor that determines the practical feasibility of the protocol.…”

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

“…Finally, it is important to mention that there have been several recent quantum repeater proposals that avoid the use of quantum memories [127,128]. These approaches typically achieve higher entanglement generation rates, but also require significantly more resources [129]. Extending upon the analysis of Ref.…”

“…Extending upon the analysis of Ref. [129], an interesting future direction could be to develop a hybrid QD-based repeater scheme which utilizes some combination of all-photonic and memorybased protocols.…”