Quantum-mechanical wave-particle duality implies that probability distributions for granular detection events exhibit wave-like interference. On the single-particle level, this leads to self-interference-e.g., on transit across a double slit-for photons as well as for large, massive particles, provided that no which-way information is available to any observer, even in principle. When more than one particle enters the game, their specific many-particle quantum features are manifested in correlation functions, provided the particles cannot be distinguished. We are used to believe that interference fades away monotonically with increasing distinguishability-in accord with available experimental evidence on the single-and on the many-particle level. Here, we demonstrate experimentally and theoretically that such monotonicity of the quantum-to-classical transition is the exception rather than the rule whenever more than two particles interfere. As the distinguishability of the particles is continuously increased, different numbers of particles effectively interfere, which leads to interference signals that are, in general, nonmonotonic functions of the distinguishability of the particles. This observation opens perspectives for the experimental characterization of many-particle coherence and sheds light on decoherence processes in many-particle systems.quantum interference | which-path information | quantum statistics T he double-slit-like (self-)interference of single particles has been observed for particles ranging from photons (1) to massive particles (2). It relies on the coherence of the singleparticle wave-function, which guarantees that the different pathways a particle can take to a detector-e.g., through the left or through the right slit in a double-slit experiment-remain indistinguishable.Interaction with the environment, however, may convey whichpath information to the environment, and then inevitably leads to decoherence (3, 4). Thereby, it jeopardizes the ideal interference pattern and induces the quantum-to-classical transition (5, 6). The stronger the decoherence, the weaker is the interference signal (3). Expectation values of observables therefore depend monotonically on the strength of decoherence, and a monotonic transition between quantum and classical expectation values takes place (2, 5-10).The superposition principle, which is responsible for the above self-interference effects, also applies to many-particle wave-functions, with entanglement (11) and many-particle interference (12) as immediate consequences. For the observation of the latter, the mutual indistinguishability of the particles is necessary and it entails, for instance, the Hong-Ou-Mandel (HOM) effect (13, 14): When a single photon is incident on each of the two input modes of a balanced beam splitter (BS), the two-particle Feynman paths of "both photons reflected" and "both photons transmitted" interfere destructively, leading to the strict suppression of the event with one particle per output mode.As particles turn distinguish...

A novel molybdate-reducing bacterium, tentatively identified as Klebsiella sp. strain hkeem and based on partial 16s rDNA gene sequencing and phylogenetic analysis, has been isolated. Strain hkeem produced 3 times more molybdenum blue than Serratia sp. strain Dr.Y8; the most potent Mo-reducing bacterium isolated to date. Molybdate was optimally reduced to molybdenum blue using 4.5 mM phosphate, 80 mM molybdate and using 1% (w/v) fructose as a carbon source. Molybdate reduction was optimum at 30 °C and at pH 7.3. The molybdenum blue produced from cellular reduction exhibited absorption spectrum with a maximum peak at 865 nm and a shoulder at 700 nm. Inhibitors of electron transport system such as antimycin A, rotenone, sodium azide, and potassium cyanide did not inhibit the molybdenum-reducing enzyme. Mercury, silver, and copper at 1 ppm inhibited molybdenum blue formation in whole cells of strain hkeem.

We demonstrate the formation of many-particle interferences of different degrees to determine the transmission of four photons of tunable indistinguishability through a four-port beam splitter array. The probability of certain output events depends nonmonotonically on the degree of distinguishability, due to distinct multiparticle interference contributions to the transmission signal.

The coherence time constitutes one of the most critical parameters that determines whether or not interference is observed in an experiment. For photons, it is traditionally determined by the effective spectral bandwidth of the photon. Here we report on multi-photon interference experiments in which the multi-photon coherence time, defined by the width of the interference signal, depends on the number of interfering photons and on the measurement scheme chosen to detect the particles. A theoretical analysis reveals that all multi-photon interferences with more than two particles feature this dependence, which can be attributed to higher-order effects in the mutual indistinguishability of the particles. As a striking consequence, a single, well-defined many-particle quantum state can exhibit qualitatively different degrees of interference, depending on the chosen observable. Therefore, optimal sensitivity in many-particle quantum interferometry can only be achieved by choosing a suitable detection scheme.

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