A Controlled Phase Gate Between a Single Atom and an Optical Photon

Distributed quantum networks will allow users to perform tasks and to interact in ways which are not possible with present-day technology. Their implementation is a key challenge for quantum science and requires the development of stationary quantum nodes that can send and receive as well as store and process quantum information locally. The nodes are connected by quantum channels for flying information carriers, i.e. photons. These channels serve both to directly exchange quantum information between nodes as well as to distribute entanglement over the whole network. In order to scale such networks to many particles and long distances, an efficient interface between the nodes and the channels is required. This article describes the cavity-based approach to this goal, with an emphasis on experimental systems in which single atoms are trapped in and coupled to optical resonators. Besides being conceptually appealing, this approach is promising for quantum networks on larger scales, as it gives access to long qubit coherence times and high light-matter coupling efficiencies. Thus, it allows one to generate entangled photons on the push of a button, to reversibly map the quantum state of a photon onto an atom, to transfer and teleport quantum states between remote atoms, to entangle distant atoms, to detect optical photons nondestructively, to perform entangling quantum gates between an atom and one or several photons, and even provides a route towards efficient heralded quantum memories for future repeaters. The presented general protocols and the identification of key parameters are applicable to other experimental systems.

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“…due to changes in the magnetic field. Adapted from (Reiserer, 2014). van Loock, 2005) such as squeezed states, see e.g.…”

Section: Quantum Light Sourcesmentioning

confidence: 99%

Cavity-based quantum networks with single atoms and optical photons

2015

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“…2C will either be reflected as a result of strong coupling, or otherwise enter the cavity on its way towards detector D B . Unlike references (33,34), for our purposes here, the cavity needs to, first, support the two optical modes shown in Fig. 2C (or else support two parallel optical modes impinging on the cavity from the same side, as in (35), which ties in with our earlier suggestion to use a single CQZE module with two optical modes).…”

Section: Methods and Resultsmentioning

confidence: 88%

“…A single 87 Rb atom trapped inside a high-finesse optical resonator by means of a threedimensional optical lattice constitutes Bob's qubit (33,34). Depending on which of its two internal ground states the 87 Rb atom is in, a resonant R-polarised photon impinging on the cavity from the left in Fig.…”

Section: Methods and Resultsmentioning

confidence: 99%

From a Quantum Paradox to Counterportation

Salih

2021

Preprint

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We uncover a new quantum paradox, where a simple question about two identical quantum systems reveals unsettlingly paradoxical answers when weak measurements are considered. Our resolution of the paradox, from within the weak measurement framework, amounts to a demonstration of exchange-free communication for the generalised protocol for sending an unknown qubit without any particles travelling between the communicating parties, i.e. counterfactually. The paradox and its resolution are reproduced from a consistent-histories viewpoint. We go on to propose a novel, experimentally feasible implementation of this counterfactual disembodied transport that we call counterportation, based on cavity quantum electrodynamics, estimating resources for beating the no-cloning fidelity limit---except that unlike teleportation no previously-shared entanglement nor classical communication are required. Our approach is several orders of magnitude more efficient in terms of physical resources than previously proposed techniques, while being remarkably tolerant to device imperfections, paving the way for an experimental demonstration. Surprisingly, while counterfactual communication is intuitively explained in terms of interaction-free measurement and the Zeno effect, we show based on our proposed scheme that neither is necessary, with implications in support of an underlying physical reality.

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“…Here, a single 87 Rb atom trapped inside a high-finesse optical resonator by means of a three-dimensional optical lattice constitutes Bob's qubit [36,37]. Depending on which of its two internal ground states the 87 Rb atom is in, a resonant R-polarised photon impinging on the cavity from the left in figure 2(C) will either be reflected as a result of strong coupling, or otherwise enter the cavity on its way towards detector D B .…”

Section: Methods and Resultsmentioning

confidence: 99%

From counterportation to local wormholes

Salih

2023

Quantum Sci. Technol.

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We propose an experimental realisation of the protocol for the counterfactual disembodied transport of an unknown qubit---or what we call counterportation---where sender and receiver, remarkably, exchange no particles. We employ cavity quantum electrodynamics, estimating resources for beating the classical fidelity limit---except, unlike teleportation, no pre-shared entanglement nor classical communication are required. Our approach is multiple orders of magnitude more efficient in terms of physical resources than previously proposed implementation, paving the way for a demonstration using existing imperfect devices. Surprisingly, while such communication is intuitively explained in terms of ``interaction-free'' measurement and the Zeno effect, we show that neither is necessary, with far-reaching implications in support of an underlying physical reality. We go on to characterise an explanatory framework for counterportation starting from constructor theory: local wormholes. Conversely, a counterportation experiment demonstrating the traversability of space, by means of what is essentially a 2-qubit exchange-free quantum computer, can point to the existence in the lab of such traversable wormholes.

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A Controlled Phase Gate Between a Single Atom and an Optical Photon

Cited by 5 publications

References 160 publications

Cavity-based quantum networks with single atoms and optical photons

Cavity-based quantum networks with single atoms and optical photons

From a Quantum Paradox to Counterportation

From counterportation to local wormholes

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