Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics

Kockum, Anton Frisk; Johansson, Göran; Nori, Franco

doi:10.1103/physrevlett.120.140404

Cited by 256 publications

(215 citation statements)

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“…They can be modified, for example, by the presence of nearby metallic or dielectric surfaces and nanospheres, metamaterials or plasmonic nanowires, among others [10][11][12][13][14][15][16][17]. This phenomenon, first described by Purcell in the 1940s [18], has been studied extensively in a variety of contexts, and most prominently in systems involving quantum optical devices [19][20][21][22].…”

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Collectively Enhanced Chiral Photon Emission from an Atomic Array near a Nanofiber

et al. 2020

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Emitter ensembles interact collectively with the radiation field. In the case of a one-dimensional array of atoms near a nanofiber, this collective light-matter interaction does not only lead to an increased photon coupling to the guided modes within the fiber, but also to a drastic enhancement of the chirality in the photon emission. We show that near-perfect chirality is already achieved for moderately-sized ensembles, containing 10 to 15 atoms. This is of importance for developing an efficient interface between atoms and waveguide structures with unidirectional coupling, with applications in quantum computing and communication such as the development of non-reciprocal photon devices or quantum information transfer channels.

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Collectively Enhanced Chiral Photon Emission from an Atomic Array near a Nanofiber

et al. 2020

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“…Although a splitting in the fluorescence spectrum (inelastic scattering) indicated the presence of the collective Lamb shift, it is not straightforward to extract the size of the shift from the size of the splitting [36,55]. In our setup, the presence of the mirror introduces interference effects that suppresses the collective decay more than the collective Lamb shift [67, 68], allowing us to clearly resolve the shift in simple reflection measurements of elastic scattering. Interestingly, it turns out that these interference effects allow us to couple the two qubits via the transmission line even when one of the qubits is unable to relax into the transmission line.Device and characterization.…”

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Large Collective Lamb Shift of Two Distant Superconducting Artificial Atoms

et al. 2019

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Virtual photons can mediate interaction between atoms, resulting in an energy shift known as a collective Lamb shift. Observing the collective Lamb shift is challenging, since it can be obscured by radiative decay and direct atom-atom interactions. Here, we place two superconducting qubits in a transmission line terminated by a mirror, which suppresses decay. We measure a collective Lamb shift reaching 0.8% of the qubit transition frequency and exceeding the transition linewidth. We also show that the qubits can interact via the transmission line even if one of them does not decay into it.Introduction. In 1947, when attempting to pinpoint the fine structure of the hydrogen atom, Lamb and Retherford [1] discovered a small energy difference between the levels 2S 1/2 and 2P 1/2 , which were thought to be degenerate according to Dirac's theory of electrons. This energy difference between the two levels can be understood when vacuum fluctuations are included in the picture, as was verified later by self-energy calculations in the framework of quantum field theory [2][3][4]. Briefly put, a hydrogen atom will emit photons which are instantaneously reabsorbed; while these "virtual" photons are not detectable by themselves, they leave their traces in the Lamb shift.The hydrogen atoms that Lamb and Retherford used for their experiment were obtained from molecular hydrogen through tungsten catalyzation. Since the conversion rate for this process was very low, the 2S 1/2 level was only populated in a few atoms. Hence, the observable effects of virtual photon processes were limited to selfinteraction; exchanges of virtual photons between atoms could not be detected. However, it was later realized that atom-atom interaction mediated by virtual photons also gives rise to an energy shift, referred to as a collective, or cooperative, Lamb shift [5][6][7][8][9]. The atom-atom interaction also underpins the collective decay known as Dicke superradiance [10,11].There are several obstacles impeding the experimental observation of the collective Lamb shift. The shift can be enhanced by using many atoms, but, if these atoms are too close together, direct atom-atom interactions (not via virtual photons) can obscure the effect. Furthermore, the interaction giving rise to the collective Lamb shift is relatively weak in three dimensions, and the shift can also be hidden by the radiative linewidth (e.g., due to the collective decay). Despite these obstacles, there have been a few experimental demonstrations of collective Lamb shifts: in xenon gas [12], iron nuclei [13], rubidium vapor [14], strontium ions [15], cold rubidium atoms [16], and potassium vapor [17]. Mostly, these experiments used developments in atomic trapping and cooling [18] that have enabled higher densities of atomic ensembles, leading to a strong coupling between atomic condensates and cavity fields [19,20]. An improved theoretical understanding [21-23] of collective Dicke states also aided some of the experiments.With the single exception of Ref.[15], these previous expe...

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“…One simply couples a Josephson-junction qubit to a transmission line, meander the line away on the chip until a wavelength distance has been reached, and then bring the waveguide back to couple to the qubit once more [161]. In such a setup, interference effects for one and multiple [165] giant atoms can be designed with greater precision than if SAWs are used.…”

Section: New Atom Sizesmentioning

confidence: 99%

Quantum Bits with Josephson Junctions

Kockum

Nori

2019

Springer Series in Materials Science

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Already in the first edition of this book [1], a great number of interesting and important applications for Josephson junctions were discussed. In the decades that have passed since then, several new applications have emerged. This chapter treats one such new class of applications: quantum optics and quantum information processing (QIP) based on superconducting circuits with Josephson junctions. At the time of writing, the most recent and comprehensive reviews of this field, which has grown rapidly in the past two decades, are Refs. [2,3]. We also recommend the reviews in Refs. [4][5][6][7][8][9][10][11][12] for additional perspectives on the field. In this chapter, we aim to explain the basics of superconducting quantum circuits with Josephson junctions and demonstrate how these systems open up new prospects, both for QIP and for the study of quantum optics and atomic physics. What is a qubit?As the name suggests, the field of QIP is concerned with information in quantum rather than classical systems. In a classical computer, the most basic unit of information is a bit, which can take two values: 0 and 1. In a quantum computer, the laws of quantum physics allow phenomena like superposition and entanglement. When discussing information processing in a quantum world, the most basic unit is therefore a quantum bit, usually called qubit, a two-level quantum system with a ground state |0 and an excited state |1 . Unlike a classical bit, which only has two possible

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Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics

Cited by 256 publications

References 169 publications

Collectively Enhanced Chiral Photon Emission from an Atomic Array near a Nanofiber

Collectively Enhanced Chiral Photon Emission from an Atomic Array near a Nanofiber

Large Collective Lamb Shift of Two Distant Superconducting Artificial Atoms

Quantum Bits with Josephson Junctions

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