Remote quantum clock synchronization without synchronized clocks

Ilo-Okeke, Ebubechukwu O.; Tessler, Louis; Dowling, Jonathan P.; Byrnes, Tim

doi:10.1038/s41534-018-0090-2

Cited by 64 publications

(41 citation statements)

References 31 publications

(48 reference statements)

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“…As such, our work provides a direct path to realise entangled networks of state-of-the-art atomic clocks over large distances [32]. Entangling clocks provides a way to perform more sensitive measurements of their average ticking frequencies [32] and to overcome current limits to their synchronisation [33].…”

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confidence: 98%

Light-matter entanglement over 50 km of optical fibre

et al. 2019

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When shared between remote locations, entanglement opens up fundamentally new capabilities for science and technology [1,2]. Envisioned quantum networks distribute entanglement between their remote matter-based quantum nodes, in which it is stored, processed and used [1]. Pioneering experiments have shown how photons can distribute entanglement between single ions or single atoms a few ten meters apart [3,4] and between two nitrogen-vacancy centres 1 km apart [5]. Here we report on the observation of entanglement between matter (a trapped ion) and light (a photon) over 50 km of optical fibre: a practical distance to start building large-scale quantum networks. Our methods include an efficient source of light-matter entanglement via cavity-QED techniques and a quantum photon converter to the 1550 nm telecom C band. Our methods provide a direct path to entangling remote registers of quantum-logic capable trapped-ion qubits [6][7][8], and the optical atomic clock transitions that they contain [9,10], spaced by hundreds of kilometers.Our network node consists of a 40 Ca + ion in a radiofrequency linear Paul trap with an optical cavity that enhances photon collection on the 854 nm electronic dipole transition. (Figure 1). A Raman laser pulse at 393 nm triggers emission, by the ion, of a photon into the cavity via a bichromatic cavity-mediated Raman transition (CMRT) [11]. Two indistinguishable processes are driven in the CMRT, each leading to the generation of a cavity photon and resulting in entanglement between photon polarisation and the electronic qubit state of the ion of the form 1/ √ 2 (|D J=5/2, mj =−5/2 , V + |D J=5/2, mj =−3/2 , H ), with horizontal (H) and vertical (V ) photon polarisation and two metastable Zeeman states of the ion (D J, mj ) [12]. The total probability of obtaining an on-demand free-space photon out of the ion vacuum chamber (entangled with the ion) is 0.5 ±0.1 [12].While the ∼ 3 dB/km losses suffered by 854 nm photons through state-of-the-art optical fibre allows for few km internode distances, transmission over 50 km would be 10 −15 . 854 nm photons are also frequencyincompatible with other examples of quantum matter, preventing the realisation of ion-hybrid quantum systems over any distance. Single photon frequency conversion to the telecom C band (1550 nm) offers a powerful general solution: this wavelength suffers the minimum fibre transmission losses (∼ 0.18 dB/km) and is therefore an ideal choice for a standard interfacing wavelength for quantum networking. Photons from solid-state memories [14], cold gas memories [15,16], quantum dots and nitrogen-vacancy centres [17] have been converted to telecom wavelengths. Frequency conversion of photons from ions has recently been performed, including to the telecom C band (without entanglement) [18], to the telecom * ben.lanyon@uibk.ac.at, † These authors contributed equally O band with entanglement over 80 m [19] and directly to an atomic Rubidium line at 780 nm [20].We inject single-mode fibre-coupled photons from the ion into a polarisat...

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Light-matter entanglement over 50 km of optical fibre

et al. 2019

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“…The origin of the Wigner phase can be understood to be due to a rotation of the coordinate system, which induces a phase in the overall state. Similar effects are seen in qubit systems with a redefinition of the coordinate system [33]. Since Alice's satellite can be moving in any direction and is moving with respect to the source satellite, it will in general include both boosts and rotations.…”

Section: A Transformation Of Statesmentioning

confidence: 80%

“…In a more realistic situation, the photons will have a spread due to diffraction and will have a superposition of different momenta p, q. All three types of states that were considered, (33), (36), and (41), in fact have the same entanglement as a maximally entangled Bell state in all frames. As discussed in Ref.…”

Section: Diffraction Effectsmentioning

confidence: 99%

“…[32] that there is a hidden assumption of a common phase reference due to the need of performing a phase sensitive measurement at both Alice and Bob. Recently, several advances have been made both on the theoretical [33] FIG. 1.…”

Section: Introductionmentioning

confidence: 99%

“…for this case. The momentum degrees of freedom are traced to remove any effect of the frequency and directional shift of the (33) with σ = 1 required to reach purities as marked. We assume a photon attenuation factor of A = 100 and the number of photons required for k purification steps to be 2 k .…”

Section: B Error Introduced By Lorentz Transformationmentioning

confidence: 99%

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Relativistic corrections to photonic entangled states for the space-based quantum network

et al. 2020

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In recent years there has been a great deal of focus on a globe-spanning quantum network, including linked satellites for applications ranging from quantum key distribution to distributed sensors and clocks. In many of these schemes, relativistic transformations may have deleterious effects on the purity of the distributed entangled pairs. In this paper, we make a comparison of several entanglement distribution schemes in the context of special relativity. We consider three types of entangled photon states: polarization, single photon, and Laguerre-Gauss mode entangled states. All three types of entangled states suffer relativistic corrections, albeit in different ways. These relativistic effects become important in the context of applications such as quantum clock synchronization, where high fidelity entanglement distribution is required.

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Bi‐Frequency Illumination: A Quantum‐Enhanced Protocol

2022

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Quantum‐enhanced, idler‐free sensing protocol to measure the response of a target object to the frequency of a probe in a noisy and lossy scenario is proposed. In this protocol, a target with frequency‐dependent reflectivity ηfalse(ωfalse)$\eta (\omega )$ embedded in a thermal bath is considered. The aim is to estimate the parameter λ=η(ω2)−η(ω1)$\lambda = \eta (\omega _2)-\eta (\omega _1)$, since it contains relevant information for different problems. For this, a bi‐frequency quantum state is employed as the resource, since it is necessary to capture the relevant information about the parameter. Computing the quantum Fisher information H relative to the parameter λ in an assumed neighborhood of λ≈0$\lambda \approx \ 0$ for a two‐mode squeezed state (HnormalQ$H_\text{Q}$), and a pair of coherent states (HnormalC$H_\text{C}$), a quantum enhancement is shown in the estimation of λ. This quantum enhancement grows with the mean reflectivity of the probed object, and is noise‐resilient. Explicit formulas are derived for the optimal observables, and an experimental scheme based on elementary quantum optical transformations is proposed. Furthermore, this work opens the way to applications in both radar and medical imaging, in particular in the microwave domain.

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Remote quantum clock synchronization without synchronized clocks

Cited by 64 publications

References 31 publications

Light-matter entanglement over 50 km of optical fibre

Light-matter entanglement over 50 km of optical fibre

Relativistic corrections to photonic entangled states for the space-based quantum network

Bi‐Frequency Illumination: A Quantum‐Enhanced Protocol

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