Wave-particle duality of quantum objects is one of the most striking features of quantum physics and has been widely studied in past decades. Developments of quantum technologies enable us to experimentally realize several quantum phenomena. Observation of wave-particle morphing behavior in the context of the quantum delayed-choice experiment (QDCE) is one of them. Adopting the scheme of QDCE, we demonstrate how the coexistence of wave and particle nature emerges as a consequence of the uncertainty in the quantum controlled experimental setup, using a five-qubit cloud-based quantum processor. We also show that an entanglement-assisted scheme of the same reproduces the predictions of quantum mechanics. We put evidence that a local hidden variable theory is incompatible with quantum mechanical predictions by comparing the variation of intensities obtained from our experiment with hidden variable predictions.
Wave-particle duality of quantum objects is one of the most striking features of quantum physics and has been widely studied in past decades. Developments of quantum technologies enable us to experimentally realize several quantum phenomena. Observation of wave-particle morphing behavior in the context of the quantum delayed-choice experiment (QDCE) is one of them. Adopting the scheme of QDCE, we demonstrate how the coexistence of wave and particle nature emerges as a consequence of the uncertainty in the quantum controlled experimental setup, using a five-qubit cloud-based quantum processor. We also show that an entanglement-assisted scheme of the same reproduces the predictions of quantum mechanics. We put evidence that a local hidden variable theory is incompatible with quantum mechanical predictions by comparing the variation of intensities obtained from our experiment with hidden variable predictions.
The puzzling properties of quantum mechanics, i.e., wave-particle duality, entanglement, and superposition, have been dissected experimentally over the past decades. However, hidden-variable (HV) models based on three classical assumptions of wave-particle objectivity, determinism, and independence strive to explain the same experiments or even defeat quantum mechanics. Meanwhile, the steady development of quantum technologies continues to enable us to test experimentally the predictions of quantum mechanics and HV theories. We report an experimental demonstration of an entanglement-assisted quantum delayed-choice scheme using a liquid nuclear magnetic resonance quantum-information processor. This experiment is based on the recently proposed scheme [R. Ionicioiu et al., Nat. Commun. 5. 3997 (2014)], which predicted different results for quantum mechanics and HV theories. In our experiments, the intensities and the visibilities of the interference are consistent with the theoretical predictions of quantum mechanics. The results show that a contradiction with the experiments is indeed appearing when all three assumptions of the HV models are combined, though any two of those assumptions are compatible with the experiments.
Wheeler's delayed-choice experiment delays the decision to observe either the wave or particle behavior of a photon until after it has entered the interferometer, and the quantum delayed-choice experiment provides the possibility of observing the wave and particle behaviors with a single experimental setup by introducing quantum control. We here propose a modified quantum delayed-choice experiment without quantum control or entanglement assistance, in which a photon can be prepared in a wave-particle superposition state and the morphing behavior of wave-to-particle transition can be observed easily. It is demonstrated that the presented scheme can allow us to rule out classical hidden-variable models in a device-independent manner via violating dimension witness. We also extend the scheme to the situation of two degrees of freedom, first constructing a hybrid quantum delayed-choice experiment which enables a photon respectively exhibits wave and particle behaviors in different degrees of freedom, and then proposing a scheme to prepare the single-photon wave-particle entanglement. This study is not only meaningful to explore the wave-particle complementarity of photons, but also provides potential for the research of the single-particle nonlocality from the perspective of the wave-particle degree of freedom.
Wave-particle duality has become one of the flagships of quantum mechanics. This counterintuitive concept is highlighted in a delayed-choice experiment, where the experimental setup that reveals either the particle or wave nature of a quantum system is decided after the system has entered the apparatus. Here we consider delayed-choice experiments from the perspective of device-independent causal models and show their equivalence to a prepare-and-measure scenario. Within this framework, we consider Wheeler's original proposal and its variant using a quantum control and show that a simple classical causal model is capable of reproducing the quantum mechanical predictions. Nonetheless, among other results, we show that, in a slight variant of Wheeler's gedanken experiment, a photon in an interferometer can indeed generate statistics incompatible with any nonretrocausal hidden variable model, whose dimensionality is the same as that of the quantum system it is supposed to mimic. Our proposal tolerates arbitrary losses and inefficiencies, making it specially suited to loophole-free experimental implementations.
Gedanken experiments help to reconcile our classical intuition with quantum mechanics and nowadays are routinely performed in the laboratory. An important open question is the quantum behavior of the controlling devices in such experiments. We propose a framework to analyze quantum-controlled experiments and illustrate it by discussing a quantum version of Wheeler's delayed-choice experiment. Using a quantum control has several consequences. First, it enables us to measure complementary phenomena with a single experimental setup, pointing to a redefinition of complementarity principle. Second, it allows us to prove there are no consistent hidden-variable theories having "particle" and "wave" as realistic properties. Finally, it shows that a photon can have a morphing behavior between particle and wave. The framework can be extended to other experiments (e.g., Bell inequality).
Wave-particle duality lies at the root of quantum mechanics and is central in the description of interferences observed with elementary objects. In a delayed-choice experiment, the decision to observe the particle or wave character of a quantum system is delayed with respect to the time at which the system enters the interferometer. This paper reviews the history of the delayed-choice idea, introduced as a challenge to a realistic explanation of the wave-particle duality. It also describes recent experimental realizations of this idea and discusses intriguing extensions, such as the duality between separability and entanglement in multiple quantum systems.
The delayed-choice experiment has long been regarded as one of the most conceptually intriguing demonstrations in quantum mechanics because the measurement configuration can be selected after a quantum system has already entered the experimental apparatus. This feature has often been interpreted as suggesting that the present measurement determines whether the quantum system behaved as a wave or as a particle in the past, thereby motivating discussions of wave–particle duality and retrocausality. This paper reexamines the delayed-choice experiment from the perspective of the Intrinsic Observability Framework (IOF). Rather than interpreting the experiment as demonstrating that the past is modified or that a quantum system intrinsically possesses either wave-like or particle-like properties prior to measurement, the IOF distinguishes between the pre-measurement domain of Potential Observability (PO) and the operational establishment of Observability through measurement. Within this framework, wave-like and particle-like behaviors are interpreted as observable representations established under different accessibility bases rather than intrinsic properties of the quantum system itself. Measurement grants accessibility, thereby establishing an observable representation according to the selected accessibility basis, within which observable values become operationally defined. Consequently, the delayed choice is understood not as selecting whether the quantum system was previously a wave or a particle, but as selecting the accessibility basis through which observability is established. From this perspective, the traditional wave–particle duality is reinterpreted as the basis dependence of observable representation rather than the coexistence of two fundamentally different physical natures. The delayed-choice experiment therefore illustrates how different accessibility bases lead to different observable representations while remaining fully compatible with the standard mathematical formalism of quantum mechanics.