<i>Colloquium</i>: Quantum networks with trapped ions

Duan, Liwei; Monroe, Christopher

doi:10.1103/revmodphys.82.1209

Cited by 503 publications

(432 citation statements)

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“…For example, for the observation of ion-photon polarisation entanglement, frequency broadening of the converted photon should play no role. For entanglement swapping between remote nodes via one-or two-photon detection [5], frequency distinguishability between photons becomes important. For schemes where remote nodes absorb photons that have been frequency converted (e.g.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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Polarisation-preserving photon frequency conversion from a trapped-ion-compatible wavelength to the telecom C-band

et al. 2017

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Given the great success in encoding, manipulating, storing and reading-out quantum information in their electronic states, trapped atomic ions represent a powerful platform with which to build, or integrate into, the nodes of quantum networks [5,6]. Indeed, an elementary quantum network consisting of ions in two traps a few meters apart, has been entangled via travelling ultraviolet photons [7]. A challenge is that most readily-accessible photonic transitions in trapped ions lie at wavelengths that suffer significant absorption loss in materials for manipulating and guiding light, thereby limiting the internode networking distance. Another challenge is that ionic transitions are fixed and narrowband, such that, except in rare cases [8], they cannot be interfaced with other examples of quantum matter to enable new ion-hybrid quantum systems [9]. Note that frequency-distinguishable quantum systems can be linked via their photons, though at the cost of reducing the efficiency of making that link [10].The aforementioned challenges could be overcome using quantum frequency conversion (QFC) [11,12]; a nonlinear optical process in which a photon of one frequency is converted to another, whilst preserving all the quantum and classical photon properties. QFC of single photons has recently been studied in a variety of contexts [13][14][15][16][17][18] and is typically achieved using three-wave mixing in a secondorder non-linear ( 2 ) crystal. It has been shown that QFC can preserve a broad range of photon properties, including first-and second-order coherence, and pre-existing photonphoton entanglement [12,19,20]. QFC could, therefore, act as a quantum photonic adapter for trapped ions, allowing their high-energy photonic transitions to be interfaced with the lower-energy photons better suited for long-distance travel through optical fibers, or with other forms of quantum matter.Interfacing trapped ions with the telecom wavelengths of 1310 nm (O band) or 1550 nm (C band) is particularly Abstract We demonstrate polarisation-preserving frequency conversion of single-photon-level light at 854 nm, resonant with a trapped-ion transition and qubit, to the 1550-nm telecom C band. A total photon in / fiber-coupled photon out efficiency of ∼30% is achieved, for a free-running photon noise rate of ∼60 Hz. This performance would enable telecom conversion of 854 nm polarisation qubits, produced in existing trapped-ion systems, with a signal-to-noise ratio greater than 1. In combination with near-future trappedion systems, our converter would enable the observation of entanglement between an ion and a photon that has travelled more than 100 km in optical fiber: three orders of magnitude further than the state-of-the-art.

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Section: Conclusion and Discussionmentioning

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Polarisation-preserving photon frequency conversion from a trapped-ion-compatible wavelength to the telecom C-band

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“…41 Linking atomic qubits with photons To scale beyond the QCCD in a modular architecture, it will likely become necessary to link separate registers of trapped ion chains with photonic interfaces. 42,43 This allows quantum gates to be performed between any qubits in the processor, regardless of their relative location, 41,44,45 while supporting fault-tolerant error correction even in the face of photonic interconnects that succeed with small probability per attempt. [44][45][46] A pair of trapped ion qubit modules (elementary logic units or ELUs) can be entangled with each other using propagating photons emitted by a subset of ions from each register, designated to be 'communication qubits'.…”

Section: Ion Trap Qubits and Wiresmentioning

confidence: 99%

Co-designing a scalable quantum computer with trapped atomic ions

2016

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The first generation of quantum computers are on the horizon, fabricated from quantum hardware platforms that may soon be able to tackle certain tasks that cannot be performed or modelled with conventional computers. These quantum devices will not likely be universal or fully programmable, but special-purpose processors whose hardware will be tightly co-designed with particular target applications. Trapped atomic ions are a leading platform for first-generation quantum computers, but they are also fundamentally scalable to more powerful general purpose devices in future generations. This is because trapped ion qubits are atomic clock standards that can be made identical to a part in 10 15 , and their quantum circuit connectivity can be reconfigured through the use of external fields, without modifying the arrangement or architecture of the qubits themselves. In this forwardlooking overview, we show how a modular quantum computer with thousands or more qubits can be engineered from ion crystals, and how the linkage between ion trap qubits might be tailored to a variety of applications and quantum-computing protocols. Quantum information processors have the potential to perform computational tasks that are difficult or impossible using conventional modes of computing. 1-3 In a radical departure from classical information, the qubits of a quantum computer can simultaneously store bit values 0 and 1, and when measured they probabilistically assume definite states. Many interacting qubits, isolated from their environment, can represent huge amounts of information: there are exponentially many binary numbers that can co-exist, with entangled qubit correlations that can behave as invisible wires between the qubits. Even in the face of Moore's Law, or the doubling in conventional computer power every year or two, the complexity of massively entangled quantum states of just a few hundred qubits can easily eclipse the capacity of classical information processing. 4 There are but a few known applications that exploit this quantum advantage, such as Shor's factoring algorithm, 5 and future quantum information processors will likely be applied to special-purpose applications. On the other hand, a quantum computer has not yet been built; therefore, new quantum applications and algorithms will likely follow from the evolution and capability of quantum hardware.In the 20 years since the advent of Shor's algorithm 5 and the discovery of quantum error correction, 6-8 there has been remarkable progress in demonstrations of entangling quantum gates on o10 qubits in certain physical systems. Current efforts aim to scale to hundreds, thousands or even millions of interacting qubits. Unlike the classical scaling of bits and logic gates, however, large quantum systems are not comparable to the behaviour of just a few qubits. Just because 2 or 4 qubits can be completely controlled with negligible errors does not mean that this system can readily scale to 4100 qubits.In the last few years, two particular quantum hardware platforms have e...

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Nanophotonic quantum phase switch with a single atom

Tiecke

Thompson

Leon

et al. 2014

Nature

550

568

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In analogy to transistors in classical electronic circuits, a quantum optical switch is an important element of quantum circuits and quantum networks [1][2][3]. Operated at the fundamental limit where a single quantum of light or matter controls another field or material system [4], it may enable fascinating applications such as long-distance quantum communication [5], distributed quantum information processing[2] and metrology [6], and the exploration of novel quantum states of matter [7]. Here, by strongly coupling a photon to a single atom trapped in the near field of a nanoscale photonic crystal cavity, we realize a system where a single atom switches the phase of a photon, and a single photon modifies the atom's phase. We experimentally demonstrate an atom-induced optical phase shift [8] that is nonlinear at the two-photon level [9], a photon number router that separates individual photons and photon pairs into different output modes [10], and a single-photon switch where a single "gate" photon controls the propagation of a subsequent probe field [11, 12]. These techniques pave the way towards integrated quantum nanophotonic networks involving multiple atomic nodes connected by guided light.A quantum optical switch [11,[13][14][15][16]] is challenging to implement because the interaction between individual photons and atoms is generally very weak. Cavity quantum electrodynamics (cavity QED), where a photon is confined to a small spatial region and made to interact strongly with an atom, is a promising approach to overcome this challenge [4]. Over the last two decades, cavity QED has enabled advances in the control of microwave [17][18][19] and optical fields [13,[20][21][22][23]. While integrated circuits with strong coupling of microwave photons to superconducting qubits are currently being developed [24], a scalable path to integrated quantum circuits involving coherent qubits coupled via optical photons has yet to emerge.Our experimental approach, illustrated in Figure 1a, makes use of a single atom trapped in the near field of a nanoscale photonic crystal (PC) cavity that is attached * These authors contributed equally to this work † vuletic@mit.edu ‡ lukin@fas.harvard.eduto an optical fiber taper [2]. The tight confinement of the optical mode to a volume V ∼ 0.4 λ 3 , below the scale of the optical wavelength λ, results in strong atom-photon interactions for an atom sufficiently close to the surface of the cavity. The atom is trapped at about 200 nm from the surface in an optical lattice formed by the interference of an optical tweezer and its reflection from the side of the cavity (see Methods Summary, SI and Fig. 1a,b). Compared to transient coupling of unconfined atoms [13, 22], trapping an atom allows for experiments exploiting long atomic coherence times, and enables scaling to quantum circuits with multiple atoms. We use a one-sided optical cavity with a single port for both input and output [8]. In the absence of intracavity loss, photons incident on the cavity are always reflected. However, a s...

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Colloquium: Quantum networks with trapped ions

Cited by 503 publications

References 65 publications

Polarisation-preserving photon frequency conversion from a trapped-ion-compatible wavelength to the telecom C-band

Polarisation-preserving photon frequency conversion from a trapped-ion-compatible wavelength to the telecom C-band

Co-designing a scalable quantum computer with trapped atomic ions

Nanophotonic quantum phase switch with a single atom

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