Distributed quantum computation based on small quantum registers

Abstract

We describe and analyze an efficient register-based hybrid quantum computation scheme. Our scheme is based on probabilistic, heralded optical connection among local five-qubit quantum registers. We assume high fidelity local unitary operations within each register, but the error probability for initialization, measurement, and entanglement generation can be very high (∼ 5%). We demonstrate that with a reasonable time overhead our scheme can achieve deterministic non-local coupling gates between arbitrary two registers with very high fidelity, limited only by the imperfections from the local unitary operation. We estimate the clock cycle and the effective error probability for implementation of quantum registers with ion-traps or nitrogen-vacancy (NV) centers. Our new scheme capitalizes on a new efficient two-level pumping scheme that in principle can create Bell pairs with arbitrarily high fidelity. We introduce a Markov chain model to study the stochastic process of entanglement pumping and map it to a deterministic process. Finally we discuss requirements for achieving fault-tolerant operation with our register-based hybrid scheme, and also present an alternative approach to fault-tolerant preparation of GHZ states.

Scaling the neutral-atom Rydberg gate quantum computer by collective encoding in holmium atoms

“…Another attractive application of collective encoding would be to use a single ensemble with a 60 qubit register as a quantum repeater, or as part of a hybrid quantum computation scheme involving small, optically connected registers [10]. The 60 qubits are sufficient for 8 logical qubits, each built from 7 physical qubits, or, for example, 5 logical qubits, each built from 5 decoherence free subspace encoded qubits, that in turn require 2 physical qubits each [47].…”

“…4. Each bit is associated with the levels |F, m (= |0 i ) and |F + 1, m (= |1 i ) with F = 4, 6, 8, or 10. We see that all states, except for the 8 with F odd and m F = ±F are assigned to qubits.…”

“…In order to realize the full potential of quantum algorithms for solving difficult computational problems it will be necessary to develop approaches which allow a large number of qubits to be interconnected. Several conceptual designs for scalable quantum computing architectures have appeared in recent years based on ion traps [5], and there is intense effort directed at scalability of other approaches including quantum dots [6], superconductors [7], linear optics [8], rare earth crystals [9], and small quantum repeaters [10].…”

Phase-noise measurements in long-fiber interferometers for quantum-repeater applications

“…While there is an active theoretical activity in developing new quantum repeaters architectures based on entanglement generation by single photon quantum interference [5,6,7,16,17,18,19], no study has addressed so far the feasibility of the implementation of such protocols in installed telecom networks with respect to phase stability. In this context, we report in this paper mea- surements of the phase noise in long fiber interferometers over short timescale.…”

Creating single collective atomic excitations via spontaneous Raman emission in inhomogeneously broadened systems: Beyond the adiabatic approximation

“…The creation of collective atomic excitations via spontaneous Raman emission plays an important role in wellknown quantum information protocols, in particular the quantum repeater [1] protocol proposed by Duan, Lukin, Cirac and Zoller (DLCZ) [2]; for other protocols based on the same process see [3,4,5,6]. The basic (idealized) scheme is as follows, cf.…”