Wave-particle duality is one of the most intriguing counterfactual concepts in quantum theory. In our common sense, the wave and particle properties of a quantum object are inseparable. However, the recent studies based on Quantum Cheshire Cat phenomena showed that separating the physical properties of a quantum object including wave and particle attributes from itself are possible in microscopic system described by two-state vector formalism. In this study, we put forward a feasible scheme to spatially separate the wave and particle attributes of two entangled photons by properly choosing the pre- and post-selection of path states. Our scheme also guarantees that the observation of wave and particle properties of the two entangled photons always obey the Bohr's complementarity principle.
Wave-particle duality is one of the most intriguing counterfactual concepts in quantum theory. In our common sense, the wave and particle properties of a quantum object are inseparable. However, the recent studies based on Quantum Cheshire Cat phenomena showed that separating the physical properties of a quantum object including wave and particle attributes from itself are possible in microscopic system described by two-state vector formalism. In this study, we put forward a feasible scheme to spatially separate the wave and particle attributes of two entangled photons by properly choosing the pre- and post-selection of path states. Our scheme also guarantees that the observation of wave and particle properties of the two entangled photons always obey the Bohr's complementarity principle.
Wave-particle duality is one of the most intriguing counterfactual concepts in quantum theory, describing how quantum entities exhibit both wave-like and particle-like behaviors. In classical intuition, physical properties are inseparable from their objective carriers, while for quantum entities, wave and particle attributes coexist simultaneously. However, recent studies on the Quantum Cheshire Cat phenomenon have shown that it is possible to separate a quantum object’s physical properties—including its wave and particle attributes—from the object itself in a microscopic system described by the two-state vector formalism. In this study, we propose a feasible scheme to spatially separate the wave and particle attributes of two entangled photons by carefully selecting pre- and post-selected states. Our scheme also ensures that the observation of the wave and particle attributes of the entangled photons always obeys Bohr’s complementarity principle.
Wave and particle are two fundamental properties of nature. The wave–particle duality has indicated that a quantum object may exhibit the behaviors of both wave and particle, depending upon the circumstances of the experiment. The major significance of wave–particle duality has led to a fundamental equation in quantum mechanics: the Schrödinger equation. At present, the principle of wave–particle duality has been deeply rooted in people’s hearts. This leads to a common-sense perception that wave property and particle property coexist simultaneously in a quantum entity, and these two physical attributes cannot be completely separated from each other. In classical physics, a similar common-sense thought is that a physical system is inseparable from its physical properties. However, this has been recently challenged and beaten by a quantum phenomenon called the “quantum Cheshire cat,” in which a cat and its grin can be spatially separated. In this work, we propose a thought experiment based on the technology similar to the quantum Cheshire cat. We find that wave and particle attributes of a quantum entity can be completely separated, thus successfully dismantling the wave–particle duality for a quantum entity. Our result is still consistent with the complementarity principle and deepens the understanding of quantum foundations.
The quantum Chesire cat has drawn quite a deal of attention over the past few years, challenging the common sense perception that a physical system is inseparable from its physical properties. In this work we propose a thought experiment based on the quantum Chesire cat, which shows that suitable pre- and post-selections can not only separate a physical system from its properties, but also even separate the wave and particle attributes of a physical system. The enduring view about the wave-particle duality has suggested that a quantum entity behaves like both a wave and a particle. However, the wave-particle duality can be spatially separated under such pre- and post-selection conditions, thus allowing us to dismantle these two fundamental attributes of nature.
As a fundamental characteristic of physical entities, wave‒particle duality describes whether a microscopic entity exhibits wave or particle attributes depending on the specific experimental setup. This assumption is premised on the notion that physical properties are inseparable from the objective carrier. However, after the concept of the quantum Cheshire cats was proposed, which makes the separation of physical attributes from the entity possible, the premise no longer holds. Furthermore, an experimental demonstration of the separation of the wave and particle attributes inspired by this scenario remains scarce. In this work, we experimentally separated the wave and particle attributes of a single photon by exploiting the quantum Cheshire cat concept for the first time. By applying a weak disturbance to the evolution of the system, we achieve an effect similar to the quantum Cheshire cat and demonstrated the separation of the wave and particle attributes via the extraction of weak values. Our work provides a new perspective for the in-depth understanding of wave‒particle duality and promotes the application of weak measurements in fundamentals of quantum mechanics.
Wave-particle duality and entanglement are two fundamental characteristics of quantum mechanics. All previous works on experimental investigations in wave-particle properties of single photons (or single particles in general) showed that a well-defined interferometer setting determines a well-defined property of single photons. Here we take a conceptual step forward and control the wave-particle property of single photons with a Bell state. By doing so, we experimentally test the complementarity principle in a scenario in which the setting of the interferometer is not defined at any instance of the experiment, not even in principle. To achieve this goal, we establish the three-photon entangled state, i.e., the entanglement between a single photon and a two-photon Bell state, send the photon of interest S into a quantum Mach-Zehnder interferometer (MZI), in which the output beam splitter of the MZI is controlled by the quantum state of the second photon C, which is entangled with a third photon A. Therefore, the individual quantum state of photon C is undefined, which implements the undefined settings of the MZI for photon S. This is realized by using three cascaded phase-stable interferometers for three photons. There is typically no well-defined setting of the MZI and thus the very formulation of the wave-particle objectivity from local hidden variable models becomes internally inconsistent.
Bohr's complementarity notion is at the heart of quantum physics. It suggests that quantum systems are observed as waves or particles depending on the type of measurement, i.e., the experimental arrangement, they are subjected to. For instance, sending single photons to an open or closed Mach-Zehnder interferometer (MZI) leads to the observation of particle or wave behaviours, respectively. In 1984, Wheeler proposed a "Gedanken" delayed-choice experiment in which the interferometer configuration is chosen at will by the experimentalist only after the photon has already passed the input beam-splitter (BS_in) of the device. This experiment was realized using a single photon source and showed that Bohr's complementarity notion was still obeyed.It was recently proposed to take Wheeler's experiment one step further by employing an output "quantum beam-splitter" (QBS), i.e.,preparing BS_out in a coherent superposition of being absent and present. This allows choosing the type of measurement, i.e., wave or particle, only after having determined the state of the QBS, which can be (in principle) infinitely delayed.We realized such an experiment by exploiting the resource of entanglement, in this case pairs of polarization entangled photons. The behaviour of one of the paired photons, called the test photon, is analysed using a MZI having a QBS at its output. This QBS is enabled by entanglement and made of a polarization dependent beam-splitter. The other photon, called the corroborative photon, allows determining the state of the QBS, and consequently, which test photon behaviour (wave, particle, or both) is observed.By manipulating the corroborative photon polarization state, we demonstrate a continuous morphing of the test photon from wave to particle behaviour. This refutes simple models of single photons behaving exclusively as waves or particles. The state of the QBS is determined via the measurement of the corroborative photon only after the test photon has already been detected. The space-like separation between the two measurements invalidates local-hidden variable models associated with pre-existing information about the measurement outcomes. In other words, when the test photon is detected, no information is available about the type of measurement it underwent. These results still perfectly obey Bohr's complementarity notion and its extension.