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Register a new userTwo methods for measuring Bell nonlocality via local unitary invariants of two-qubit systems in Hong-Ou-Mandel interferometers
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We describe a direct method to experimentally determine local two-qubit invariants by performing interferometric measurements on multiple copies of a given two-qubit state. We use this framework to analyze two different kinds of two-qubit invariants of Makhlin and Jing et. al. These invariants allow to fully reconstruct any two-qubit state up to local unitaries. We demonstrate that measuring 3 invariants is sufficient to find, e.g., the optimal Bell inequality violation. These invariants can be measured with local or nonlocal measurements. We show that the nonlocal strategy that follows from Makhlins invariants is more resource-efficient than local strategy following from the invariants of Jing et al. To measure all of the Makhlins invariants directly one needs to use both two-qubit singlet and three-qubit W-state projections on multiple copies of the two-qubit state. This problem is equivalent to a cordinate system handness measurement. We demonstrate that these 3-qubit measurements can be performed by utilizing Hong-Ou-Mandel interference which gives significant speedup in comparison to the classical handness measurement. Finally, we point to potential application of our results in quantum secret sharing.
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We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of singlet projections performed on up to four qubit pairs. In particular, our method permits the application of the Peres-Horodecki separability criterion to an arbitrary two-qubit state. We explicitly demonstrate that measuring entanglement in terms of negativity requires three measurements more than detecting two-qubit entanglement. The reported minimal set of interferometric measurements provides a complete description of bipartite quantum entanglement in terms of two-photon interference. This set is smaller than the set of 15 measurements needed to perform a complete quantum state tomography of an arbitrary two-qubit system. Finally, we demonstrate that the set of 9 Makhlins invariants needed to express the negativity can be measured by performing 13 multicopy projections. We demonstrate that these invariants are both a useful theoretical concept for designing specialized quantum interferometers and that their direct measurement within the framework of linear optics does not require performing complete quantum state tomography.
Nearly 30 years ago, two-photon interference was observed, marking the beginning of a new quantum era. Indeed, two-photon interference has no classical analogue, giving it a distinct advantage for a range of applications. The peculiarities of quantum physics may now be used to our advantage to outperform classical computations, securely communicate information, simulate highly complex physical systems and increase the sensitivity of precise measurements. This separation from classical to quantum physics has motivated physicists to study two-particle interference for both fermionic and bosonic quantum objects. So far, two-particle interference has been observed with massive particles, among others, such as electrons and atoms, in addition to plasmons, demonstrating the extent of this effect to larger and more complex quantum systems. A wide array of novel applications to this quantum effect is to be expected in the future. This review will thus cover the progress and applications of two-photon (two-particle) interference over the last three decades.
Hong-Ou-Mandel (HOM) interference, i.e. the bunching of indistinguishable photons at a beam splitter is a staple of quantum optics and lies at the heart of many quantum sensing approaches and recent optical quantum computers. Although originally proposed as a method for sensing micron-scale variations in photon propagation path lengths and despite the detection of photon bunching using camera technologies, the technique is still to be extended to the imaging domain. We report a full-field, scan-free, quantum imaging technique that exploits HOM interference to reconstruct the surface depth profile of transparent samples. We measure both the bunched and anti-bunched photon-pair distributions at the HOM interferometer output which are combined to provide a lower-noise image of the sample. This approach demonstrates the possibility of HOM microscopy as a tool for label-free imaging of transparent samples in the very low photon regime.
Guided-wave platforms such as fiber and silicon-on-insulator waveguide show great advances over traditional free space implementations in quantum information technology for significant advantages of low transmission loss, low cost, integrability and compatible with mature fiber communication systems. Interference between independent photon sources is the key to realize complex quantum systems for more sophisticated applications such as multi-photon entanglement generation and quantum teleportation. In this work, we report Hong-Ou-Mandel interference between two independent all fiber photon pair sources over two 100GHz dense wave division multiplexing channels, the visibility reaches 53.2(8.4)% (82.9(5.3)%) without (with) back ground counts subtracted. In addition, we give a general theoretical description of the purity of the photon pair generation in dispersion shifted fiber and obtain the optimized condition for high purity photon pair generation. We also obtain a maximum coincidence to back ground ratio of 131 by cooling the fiber in liquid nitrogen. Our study shows great promising of integrated optical elements for future scalable quantum information promising.
We propose an experimental scheme to implement a second-order nonlocal superposition operation and its variants by way of Hong-Ou-Mandel interference. The second-order coherent operations enable us to generate a NOON state with high particle number in a heralded fashion and also can be used to enhance the entanglement properties of continuous variable states. We discuss the feasibility of our proposed scheme considering realistic experimental conditions such as on-off photodetectors with nonideal efficiency and imperfect single-photon sources.
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