Wheeler's delayed-choice experiment was conceived to illustrate the paradoxical nature of wave-particle duality in quantum mechanics. In the experiment, quantum light can exhibit either wavelike interference patterns or particlelike anticorrelations, depending upon the (possibly delayed) choice of the experimenter. A variant known as the quantum eraser uses entangled light to recover the lost interference in a seemingly nonlocal and retrocausal manner. Although it is believed that this behavior is incompatible with classical physics, here we show that, using postselection, the observed quantum phenomena can be reproduced by adopting a simple deterministic detector model and supposing the existence of a random zero-point electromagnetic field.
Quantum nonlocality is explored in a proposed experiment simpler than most in that only one photon is detected and no polarizations are measured. A pair of multilevel atoms is irradiated by a weak tuned laser pulse, exciting a certain level in one of them that subsequently decays to a metastable level, emitting a photon. The photon is detected on a distant screen, producing an interference pattern. In the delayed-choice option a second tuned laser pulse that indirectly deexcites the metastable level is sent in later, but while the photon is in flight toward the screen. The interference pattern is found to be erased. A feature is that this ``memory erasure'' is partial, and its degree is controlled by varying the distance between the pair of atoms.
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.