Abstract Nowadays the most intriguing features of wave-particle complementarity of single-photons are exemplified by the famous Wheeler’s delayed-choice experiment with linear optics, nuclear magnetic resonance, and integrated photonic device systems in the optical platform. Until now, the delayed-choice experiments are demonstrated by either massless photons or massive particles, such as atoms, however, there is no report demonstrating Wheeler’s ideas in a hybrid system which consists of photons and atoms simultaneously. Here, we demonstrate a Wheeler’s delayed-choice experiment in an interface of light and atomic memory, in which the cold atomic memory makes the heralded single-photon divided into a superposition of atomic collective excitation and leaked pulse, thus acting as memory-based beam-splitters. We observe the intermediate states between particle and wave behavior by changing the relative proportion of the quantum random number generator, the second memory efficiency, and the relative storage time of two memories. The reported results confirm Bohr’s view that it makes no sense to illustrate the wave-like or particle-like behavior of light and matter before the measurement happens, and are helpful for improving our comprehension of the complementarity principle under the interface of light-atom interaction.
Abstract Nowadays the most intriguing features of wave-particle complementarity of single-photons are exemplified by the famous Wheeler’s delayed-choice experiment with linear optics, nuclear magnetic resonance, and integrated photonic device systems in the optical platform. Until now, the delayed-choice experiments are demonstrated by either massless photons or massive particles, such as atoms, however, there is no report demonstrating Wheeler’s ideas in a hybrid system which consists of photons and atoms simultaneously. Here, we demonstrate a Wheeler’s delayed-choice experiment in an interface of light and atomic memory, in which the cold atomic memory makes the heralded single-photon divided into a superposition of atomic collective excitation and leaked pulse, thus acting as memory-based beam-splitters. We observe the intermediate states between particle and wave behavior by changing the relative proportion of the quantum random number generator, the second memory efficiency, and the relative storage time of two memories. The reported results confirm Bohr’s view that it makes no sense to illustrate the wave-like or particle-like behavior of light and matter before the measurement happens, and are helpful for improving our comprehension of the complementarity principle under the interface of light-atom interaction.
Abstract The delayed choice gedanken-experiment initially proposed by J A Wheeler reveals the nontrivial features of wave–particle duality in quantum world, that is, the choice of whether to observe the particle/wave character of a quantum system at a delayed time can affect its evolution history. In this work, the Wheeler’s delayed-choice experiment is conducted and tested in a new regime based on a Rydberg-ground level atomic Mach–Zehnder interferometer with optical coherent manipulation. Our quantum system exhibits an excellent single-excitation of the collective atomic state due to the Rydberg blockade effect, and the delayed choice of the interferometer configuration is realized by a quantum random number generator based on high-quality Rydberg single-photon source. Our experimental results demonstrate the Wheeler’s nontrivial time order inversion in this quantum system and confirm the Copenhagen interpretation of the physical reality of quantum state, which means the particle/wave character can only be ascribed to a quantum system when it was measured. This work is encouraging toward testing the foundations of quantum mechanics using the Rydberg atoms.
Wheeler's delayed-choice experiment demonstrates wave-particle duality of particles using different experimental configurations of a Mach-Zehnder interferometer. In a quantum version of this experiment, the wave-particle behavior of photons can be observed by controlling presence or absence of the second beam splitter. Here, we implement a delayed-choice experiment with dual selections based on entangled photons, experimentally controlling both of two beam splitters in the Mach-Zehnder interferometer, where the presence and absence of the second beam splitter are simultaneously controlled through path encoding. Our experiment reveals the wave-particle behavior of single photons under different configurations of two beam splitters. We further discuss the scenario when two beam splitters are in a quantum superposition of being present and absent, photons will be in a wave-particle quantum superposition state.
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.
Bohr's complementarity notion is at the heart of quantum physics, and suggests that in a quantum experiment, the observed phenomena are inherently linked to the type of measurement that is performed. For example, sending single photons to an open or closed Mach-Zehnder interferometer leads to the observation of particle or wave behaviours. In 1984, Wheeler proposed a 'Gedanken' experiment in which the experimentalist chooses the interferometer configuration, at will, only after the photon has already passed the input beam-splitter (BSin) of the device. This experiment was realized using a diamond-based single photon source, and it was shown that Bohr's complementarity notion was still obeyed, as expected. It was recently proposed theoretically to take Wheeler's experiment one step further by employing a 'quantum beam-splitter' (QBS) at the interferometer output. In this case, the output beam-splitter (BSout) is placed in a coherent superposition of being absent and present, which also allows to further delay the choice of the measurement type. The type of measurement is determined only after having measured the state of the QBS, which can be (in principle) infinitely delayed. We demonstrate the realization of such an experiment by exploiting entanglement. In particular, we take advantage of pairs of polarization entangled photons. The behaviour of one of the paired photons, called the test photon, is analysed by sending it to a Mach-Zehnder interferometer having an entanglement-enabled QBS at its output. This device is made of a polarization dependent beam-splitter followed by polarization state erasers. The other photon, called the corroborative photon, allows determining the actual state of the QBS, and consequently, which test photon behaviour (wave, particle, or both) is measured. By manipulating the corroborative photon, we demonstrate a continuous morphing from wave to particle behaviour, which refutes too simple views of single photons behaving exclusively as waves or particles. The measurements on the test photon and the interferometer configuration are performed in a strictly delayed manner. The state of the QBS is measured only after the test photon already left the interferometer, and is detected, which means that it is destroyed before the type of measurement it under- goes is determined. We find that even in this configuration, Bohr's complementarity notion, and its extension, are perfectly obeyed. The space-like separation between the measurements invalidates local-hidden variable models associated with pre-existing information about the measurement out- comes. In other words, when the test photon is detected, no information is available about the type of measurement that was performed. This assertion is confirmed by the violation of the Bell's inequalities with more than 10 standard deviations. The presence of entanglement shows furthermore that genuine quantum behaviour for the test photons has been observed. As a conclusion, we have demonstrated the experimental realization of the quantum version of Wheeler's experiment. Trying to explain our observations in classical terms causes severe contradictions, but the results are in perfect agreement with quantum physics, in which the measurement timing order does not matter. The beauty in such experiments is that space and time do not seem to play any role.
Wheeler's delayed-choice experiment highlights strange features of quantum theory such as pre-sensing of the experimental setup by the quantum object and the role of time. A recent proposal for such an experiment with an interferometer having a quantum beam splitter (QBS) [R. Ionicioiu and D. R. Terno, Phys. Rev. Lett. 107, 230406 (2011)] and its subsequent experimental implementations through photonics and NMR have produced results including the modification in the concept of complementarity. Here we propose a matter-wave Mach-Zehnder-Bragg cavity-QED interferometric setup with final QBS engineered through a cavity field that is taken initially in the superposition of zero and one photon. The setup operates through first-order off-resonant Bragg diffraction of the neutral atoms from the cavity fields with the matter wave's particle (wave) nature marked through the absence (presence) of a photon in the final cavity. The proposal, addressing the issue through atomic de Broglie waves, can be executed within the present cavity-QED experimental scenario with appreciable success probability and fidelity.
Light's wave-particle duality is at the heart of quantum mechanics and can be well illustrated by Wheeler's delayed-choice experiment: The choice of inserting or removing the second classical (quantum) beam splitter in a Mach-Zehnder interferometer determines the classical (quantum) wave-particle behavior of a photon. In this paper, we report our experiment on directly observing simultaneous wave and particle behavior in a narrowband single-photon wave packet by classically inserting or removing the second beam splitter when part of the wave packet passes through it. Our experiment demonstrates that the produced wave-particle state can be utilized in encoding quantum information.