Quantum objects, sometimes called quantons, often display a characteristic feature referred to as wave-particle duality (WPD). Lately, this and other quantum traits have been subjected to intensive research, mainly motivated by the development of quantum information science. As a consequence, the scopes of some concepts have been extended, and it has been realized that they are not in the exclusive domain of quantum physics. This is particularly clear in optics, where qubits may show up as Jones vectors and WPD has its counterpart as wave-ray duality. WPD was originally addressed by focusing on a single qubit, which was afterwards supplemented with a second one playing the role of a path-marker in an interferometer setup. Fringe contrast, a sign of wave-like behavior, was proved to be diminished in connection with the effectiveness of the marker, the inducer of particle-like behavior. Going from bipartite to tripartite states is a natural and necessary step towards better understanding of WPD. This step is what we have accomplished in this work. We report some constraints ruling WPD for tripartite systems, as well as their experimental display with single photons.
The quantification of wave-particle duality (WPD) by means of measurable features associated to it, such as fringe visibility (
V) and path distinguishability (
D), led to the establishment of the constraint
V2+D2≤1. The two involved quantities refer to so-called "quantons", physical objects that are capable of generating an interferometric pattern, while being at least partially localizable. Any quanton's internal degree of freedom (DOF) can in principle be used as a path-marker. When the quanton and its internal DOF are simultaneously engaged, new constraints can be derived and experimentally tested. Generalized constraints show how
V and
D relate to other quantifiers and bring to light coherences that might remain otherwise hidden in both quantum and classical light. We submitted two-qubit constraints to experimental tests, using optical light beams. This shows that, despite the rather contrived nature of the constraints, linear optics setups are appropriate to test them. Our experimental results are in very good agreement with theoretical predictions related to the tested constraints. Our results also show that quantifiers such as
V and
D help not only to quantify, but also to generalize the concept of WPD.
Wave-particle duality (WPD) of photons is a recurrent topic in science education research in teaching and learning the quantum behaviour of light. In this commentary, we discuss how WPD has been approached in science teaching and science education literature, and how it leads to ontological challenges in searching for the real “nature of photons”. We suggest that WPD can serve as a starting point of teaching quantum physics if we want to use natural language in discussing experimental results (as Bohr intended it to be). That way WPD can also be approached as part of modern quantum optics as a natural language expression to communicate information acquired in experiments. Such an ap-proach includes a contemporary understanding of quantitative WPD as a means to speak about features of photons as quantum states, not as entity-like objects. Content is discussed at a level appropriate for physics teacher education.
Photons in a two-path interferometer best embody wave-particle duality (WPD), which is a core concept of quantum theory. So far, the WPD relation is commonly written as
V2+D2≤1, where
V is the interference fringe visibility and
D is path distinguishability, i.e., the distinguishability of which path a photon passed. This inequality is saturated only when the which-way marker (WWM), which embodies which-path information (WPI) via an internal degree of freedom of photons, such as polarization, is in a pure state. For mixed-state WWM, conventionally defined distinguishability underestimates the amount of WPI and thus does not saturate the WPD relation. Here, we introduce a generalized measure of distinguishability
D that properly quantifies the WPI and saturates the WPD relation for all pure- and mixed-state WWM within a purification-based framework. To this end, mixed-state WWM is treated as a result of entanglement formation between the WWM and an external degree of freedom, e.g., environment, and
D is defined so that it incorporates the total WPI shared between the WWM and the environment. We show that
D thus defined is experimentally quantifiable, independently of
V, without access to the environment. We experimentally evaluate
V and
D using true single photons generated in the completely mixed (unpolarized) state, and thus verify the saturated WPD relation.
Abstract Scientific terms and concepts sometimes evolve so that their semantic meanings are changing, to better serve the purposes of their use in scientific practices. Acknowledging the importance of such a process provides a viewpoint on the role of wave-particle duality (WPD) in modern quantum optics and how it is connected to its historical role. The transformation of WPD into a quantitative and operationalised concept is approached here from the viewpoint of the role of WPD as a linguistic practice based on natural language in communicating about experiments and their results and designs. The perspective adopted is based on semantic change and variation of WPD as driven by its role as natural language expression in pursuing the epistemic and the pragmatic goals of the inquiry. This provides a perspective that connects the historical and contemporary roles of WPD through its pragmatic linguistic role. This perspective shifts the focus from philosophical realism-driven questions about WPD as related to the nature or behaviour of photons to questions of how that concept is used in practices of quantum optics research, for what purposes, and with what benefits.
Abstract A global multi-partite entanglement may place a constraint on the wave-particle duality. We investigate this constraint relation of the global entanglement and the quantitative wave-particle duality in tripartite systems. We perform quantum state tomography to reconstruct the reduced density matrix by using the OriginQ quantum computing cloud platform. As a result, we show that, theoretically and experimentally, the quantitative wave-particle duality is indeed constrained by the global tripartite entanglement. The present constraint relation can not only provide the foundational explanation for experimentally testing wave-particle duality, and also give the global entanglement a motivated physical meaning from the point of view of the quantitative wave-particle duality.
One of the most puzzling consequences of interpreting quantum mechanics in terms of concepts borrowed from classical physics, is the so-called wave-particle duality. Usually, wave-particle duality is illustrated in terms of complementarity between path distinguishability and fringe visibility in interference experiments. In this work, we instead propose a new type of complementarity, that between the continuous nature of waves and the discrete character of particles. Using the probabilistic methods of quantum field theory, we show that the simultaneous measurement of the wave amplitude and the number of photons in the same beam of light is, under certain circumstances, prohibited by the laws of quantum mechanics. Our results suggest that the concept of “interferometric duality'' could be eventually replaced by the more general one of “continuous-discrete duality''.