Precision Measurement of Electronic Ion-Ion Interactions between NeighboringEu3+Optical Centers

Abstract

We report measurements of discrete excitation-induced frequency shifts on the 7 F 0 ! 5 D 0 transition of the Eu 3þ center in La:Lu:EuCl 3 Á 6D 2 O resulting from the optical excitation of neighboring Eu 3þ ions. Shifts of up to 46:081 AE 0:005 MHz were observed. The magnitude of the interaction between neighboring ions was found to be significantly larger than expected from the electric dipole-dipole mechanism often observed in rare earth systems. We show that a large network of interacting and individually addressable centers can be created by lightly doping crystals otherwise stoichiometric in the optically active rare earth ion, and that this network could be used to implement a quantum processor with more than ten qubits. DOI: 10.1103/PhysRevLett.111.240501 PACS numbers: 03.67.Lx, 42.50.Md, 78.47.nd Rare earth ions in solids are increasingly being utilized in demonstrations of quantum information devices. In particular, a broad range of protocols for realizing memories in these materials have been developed, using controlled reversible inhomogeneous broadening [1,2], atomic frequency combs [3,4], rephased amplified spontaneous emission [5] or silencing of a photon echo ([6,7]). The first demonstration of a quantum memory operating above the no cloning limit [8], and the first demonstration of storage for over a second [9], were performed in a rare earth doped material. Very large bandwidths [10] and multi-mode capacity [11] have been achieved and the ability to store polarization qubits demonstrated [12][13][14]. Rare earth solids are successful as quantum memories because they combine high spectral and spatial densities with long optical and hyperfine coherence times, properties that are almost unique to rare earth ions amongst all optical centers in solids.All of the above devices operate on the assumption that the rare earth ions are isolated from one another, interacting only through the optical field. This is a reasonable approximation for the low concentration crystals used for the quantum memory demonstrations to date, but as the rare earth ion concentration is increased to increase memory bandwidths and efficiencies, ion-ion interactions will increasingly become important.Although the interaction between ions is likely to degrade the performance of quantum devices requiring ensembles of isolated optical centers, there has been interest in utilizing electronic ion-ion interactions to perform quantum logic operations [15,16]. The experimental investigations to date have been carried out using an ensemble approach (e.g., Refs. [17][18][19][20]), but recent demonstrations of the detection of single rare earth ion dopants [21,22] has raised the prospect of developing single instance quantum processors based on rare earth ions. Electronic interactions between rare earth ions in crystals are not well characterized. They are studied through two main effects: energy transfer between ions and optical frequency shifts caused by the excitation of nearby ions. Most studies of both these effects have been mad...

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“…18 Large and switchable interactions between RE ions have also been observed, 19 as well as single RE detection, 20,21 which opens the way to quantum processing in these systems.…”

Quantum processing with ensembles of rare-earth ions in a stoichiometric crystal

“…For multi-qubit gates, we use the strong diagonal inter-action on the optical transition, where the change in the wavefunction after exciting the first ion shifts the optical transition frequency of the second ion [25]. This interaction is both strong and homogeneous: in EuCl 3 ·6H 2 O, we measured interactions between different pairs of satellite lines to be O(10 MHz) with a homogeneity better than 1 kHz (the instrument limit) [25]. Importantly, there is no significant interaction with hyperfine spin transitions, because the Stark shift of spin levels, O(1 Hz.cm/V) [26] is much smaller than optical transitions O(10-100 kHz.cm/V) [27].…”

Theory of cavity-enhanced nondestructive detection of photonic qubits in a solid-state atomic ensemble

“…Having sufficiently many ions in the cavity to be able to store N p = 6000 photons as suggested above probably requires an increase in the cavity length by at least an order of magnitude, taking into account the fact that the AFC memory protocol requires spectral tailoring, which reduces the available number of atoms. Another attractive way to increase the number of atoms would be to use recently developed stoichiometric rareearth crystals [33,34] where ultranarrow inhomogenous linewidth has been observed. However, currently these crystals are made only from weak dipole elements like Eu 3+ which is not good for our proposal.…”