Quantum uncertainty and a counterexample of nonlocal classical “realism”

We analyze the scheme of an experiment in which, by examining suppression effects of the cross correlation of photons in a beamsplitter and by preparing squeezed states, it is proven that the phase difference of photons in Fock states cannot acquire a certain value, since, otherwise, the simultaneous existence of these two effects would be impossible. We show that this reveals an intrinsic inconsistency of the nonlocal classical interpretation of quantum mechanics on the basis of nonlocal classical “realism.”     

Generation of entangled states of qudits using twin photons

We report an experiment to generate entangled states of D-dimensional quantum systems, qudits, by using transverse spatial correlations of two parametric down-converted photons. Apertures with D slits in the arms of the twin photons define the qudit space. By manipulating the pump beam correctly, the twin photons will pass only by symmetrically opposite slits, generating entangled states between these different paths. Experimental results for qudits with D = 4 and 8 are shown. We demonstrate that the generated states are entangled states.     

Lorentz violation and black-hole thermodynamics: Compton scattering process

A Lorentz-noninvariant modification of quantum electrodynamics (QED) is considered, which has photons described by the nonbirefringent sector of modified Maxwell theory and electrons described by the standard Dirac theory. These photons and electrons are taken to propagate and interact in a Schwarzschild spacetime background. For appropriate Lorentz-violating parameters, the photons have an effective horizon lying outside the Schwarzschild horizon. A particular type of Compton scattering event, taking place between these two horizons (in the photonic ergoregion) and ultimately decreasing the mass of the black hole, is found to have a nonzero probability. These events perhaps allow for a violation of the generalized second law of thermodynamics in the Lorentz-noninvariant theory considered.     

Distinguishing N Photons in an Entangled State from N Separate Photons

We present a multimode model to describe an arbitrary N-photon state. In general, the N photons can be distinguished through their temporal modes. From this model, we can find the criterion for the N photons in an indistinguishable state of a single temporal mode. We find that simple multi-photon detection scheme cannot distinguish N photons in different temporal modes and only a multi-photon interference experiment can accomplish the goal. We apply the theory to the four-photon case in the process of parametric down-conversion. We will present the results for various four-photon interference schemes and identify a quantity to characterize how well the four photons are indistinguishable.     

Quantum theory and the nature of interference

It is shown that many of the difficulties associated with the Copenhagen interpretation of quantum theory are resolved by a new interpretation of interference derived from solutions to Maxwell's equations. An infinite wave model of the photon based on these solutions is described and used to explain the interference of single photons as well as the corpuscular behavior evident in the Compton and photoelectric effects. The wave-particle duality and the uncertainty relations are also discussed. According to the new interpretation of interference in a Young's double-slit experiment, photons which pass through the left-hand slit always arrive in the left-hand part of the screen and no photons pass into this area via the right-hand slit. This conclusion is compared with the viewpoint of the Copenhagen school and an experiment to distinguish between them is suggested.     

Event‐by‐event simulation of quantum phenomena

A discrete‐event simulation approach is reviewed that does not require the knowledge of the solution of the wave equation of the whole system, yet reproduces the statistical distributions of wave theory by generating detection events one‐by‐one. The simulation approach is illustrated by applications to a two‐beam interference experiment and two Bell test experiments, an Einstein‐Podolsky‐Rosen‐Bohm experiment with single photons employing post‐selection for pair identification and a single‐neutron Bell test interferometry experiment with nearly 100 % detection efficiency.     

Review of recent experimental progress in foundations of quantum mechanics and quantum information achieved in parametric downconversion experiments at IENGF

We review some recent experimental progress concerning foundations of quantum mechanics and quantum information obtained in the Carlo Novero Quantum Optics Laboratory at IENGF. After a short presentation of our polarization-entangled photon source (based on precise superposition of two type I PDC emissions) and of the results obtained with it, we describe in more detail an innovative double slit experiment where two degenerate photons produced by PDC are each sent to a specific slit. Beyond representing an interesting example of the relation between the visibility of interference and welcher Weg knowledge, this configuration has been suggested for testing de Broglie-Bohm theory (dBB) against standard quantum mechanics (SQM). Our results perfectly fit SQM results but disagree with dBB predictions. Then, we discuss a recent experiment addressed at clarifying the issue of which wave-particle observables are really to be considered when discussing wave-particle duality. This experiments realizes the theoretical proposal of Agarwal et al., overcoming the limitations of a previous experiment. Finally, we hint at the realization of a high-intensity high-spectral-selectivity PDC source to be used for quantum information studies.     

Angular correlation of scattered annihilation photons, to test the possibility of hidden variables in quantum theory

Angular correlations of the annihilation photons, Compton scattered by plastic scintillators and detected by means of NaI (T1) crystals, have been measured in order to test the possibility of deviations of the experimental results from the predictions of the quantum theory. In fact, Jauch and Bohm, starting with different motivations, both arrive at the possibility of a lower correlation ratio between the two orthogonal polarization states of the two photons than predicted by quantum theory. This in turn should give a lower azimuthal anisotropy in the angular correlations. Our experimental results compared with the theoretical predictions, after correction for finite geometry by means of a Montecarlo method, do not confirm quantum theory and exclude the hypotheses of Jauch and of Bohm. We are continuing the experiment in order to test wether the breakdown in the polarization correlation depends on the distance (spatial and/or temporal) between the two correlated scattering events, as suggested by Jauch. Paper A 34 presented at 3 rd Internat'l Conf. Positron Annihilation, Otaniemi, Finland (August 1973).     

Derivation of generalized quantum jump operators and comparison of the microscopic single photon detector models

The recent experiment of Parigi et al. [Science 317, 1890 (2007)] shows, in agreement with theory, that subtraction of one photon can increase the expectation value of the number of photons in the thermal state. This observation agrees with the standard photon counting model in which the quantum jump superoperator (QJS) gives a count rate proportional to the number of photons. An alternate model for indirect photon counting has been introduced by Dodonov et al. [Phys. Rev. A 72, 023816 (2005)]. In their model the count rate is proportional to the probability that there are photons in the cavity, and the cavity field is bidirectionally coupled with a two state quantum system which is unidirectionally coupled to a counting device. We give a consistent first principle derivation of the QJSs for the indirect photon counting scheme and establish the complete relations between the physical measurement setup and the QJSs. It is shown that the time-dependent probability for photoelectron emission event must include normalization of the conditional probability. This normalization was neglected in the previous derivation of the QJSs. We include the normalization and obtain the correct photoelectron emission rates and the correct QJSs and show in which coupling parameter regimes these QJSs are applicable. Our analytical results are compared with the exact numerical solution of the Lindblad equation of the system. The derived QJSs enable analysis of experimental photon count rates in a case where a one-to-one correspondence does not exist between the decay of photons and the detection events.     

Polarization of Photons under Conditions of Interference between the Parametric Radiation and Coherent Bremsstrahlung

X rays emitted by relativistic electrons traversing a system of parallel atomic planes of a crystal are considered. The spectral, angular, and polarization characteristics of emitted photons are studied theoretically simultaneously for two coherent emission mechanisms, namely, the coherent bremsstrahlung and parametric X rays. Based on the results obtained, an optimal design of the experiment on studying the effect of interference of these emission mechanisms on the polarization of photons is calculated. The developed experimental facility is described.     

Absorption cross-section fluctuations driven by continuous and discrete laser frequency variations

Though the operational definition of a photon’s absorption cross-section is straightforward, the definition has a fundamental and well-known subtlety. In order to make contact with theory, the incident photons must be monoenergetic and should impinge on the target atom or molecule at a constant rate. To some extent, however, these two constraints are always violated: no field is perfectly monochromatic and laser photons bunch (for both technical and fundamental reasons). Thus, the textbook definition of cross-section must be understood in terms of a mean, in which case the quantum nature of a field and the practicability of its realization must be recognized as sources of cross-section variance. Here, we consider the role that continuous and discrete random frequency fluctuations play in determining the variance of an absorption cross-section. In particular, we investigate the differing roles of phase diffusion and mode-partition noise, finding that discontinuous mode variations have a significant and not easily discerned effect on an absorption cross-section’s variance. As a by-product of our studies, agreement between theory and experiment highlights the utility of a hybrid absorption cross-section for use in the quasi-static approximation, and also suggests an exponential relationship between the rate of mode hops and injection current in cleaved-facet diode lasers.     

Experimental nonlinear sign shift for linear optics quantum computation

We have realized the nonlinear sign shift operation for photonic qubits. This operation shifts the phase of two photons reflected by a beam splitter using an extra single photon and measurement. We show that the conditional phase shift is (1.05+/-0.06)pi in clear agreement with theory. Our results show that, by using an ancilla photon and conditional detection, nonlinear optical effects can be implemented using only linear optical elements. This experiment represents an essential step for linear optical implementations of scalable quantum computation.     

Dynamic theory of two-photon correlators in the spectroscopy of single impurity centers

A dynamic theory of two-photon correlators measured in experiments with single molecular impurity centers has been developed. The theory takes into account the interaction between optically active electrons of an impurity center and phonons, excitations in tunneling systems of polymers and glasses, and transverse electromagnetic field. Both the correlator measured in the start-stop regime and the “full” correlator have been analyzed, and equations for these correlators have been derived. An equation relating these two correlators has been also obtained. The effect of the triplet level of an impurity molecule on the correlators leading to bunching of spontaneously emitted photons has been studied. The two-photon correlators have been calculated numerically, and their dependence on the incident light frequency and time between the pairs of detected photons in various realistic situations has been derived. Zh. éksp. Teor. Fiz. 113, 1606–1631 (May 1998)     

群速度色散对于纠缠光场二阶关联函数影响的研究

HBT干涉是量子测量中的一种重要手段, 其通过计算光场的二阶关联函数而得到测量结果. 在长距离测距中, 光场的二阶关联函数会受到光纤中群速度色散的影响而发生展宽和平移, 从而在一定程度上影响测量精度. 本文主要针对二阶关联函数半高宽受群速度色散的影响, 给出了半高宽与测量距离与群速度色散系数的关系.     

Enhanced Nonclassical Third-Order Spatial Intensity Correlations in Three-Beam Interferences<

The joint probability of detecting simultaneously three photons at two and three points in the superposition field of three independent plane waves with the same frequency but random phases is calculated and compared with the results of a classical wave theory. Significant differences occur for sufficiently weak fields. We find that the differences between the quantum mechanical and classical predictions concerning the third order intensity correlation functions are more pronounced in a three-beam than in a two-beam interference experiment.     

Preselection with certainty of photons in a singlet state from a set of independent photons

It is shown that one canpreselect with certainty photons in the singlet state from a set of completely unpolarized and independent photons which did not in any way directly interact with each other-without in any way affecting them. The result is based on an experiment which puts together two unpolarized photons from two independent singlet pairs, making them interfere in the fourth order at a beam splitter so as to preselect the singlet state of the other two photons from the pairs, although no polarization measurement has been carried out on the photons coming out from the beam splitter. One can obtain the expectation value for the correlated state of the former two unpolarized photons in the Hilbert space and therefore write down the singlet state for them, but one apparently cannotinfer the state within the Hilbert space. This might suggest that the Hilbert space is not amaximal model for quantum measurements.     

Erasing distinguishability using quantum frequency up-conversion

The frequency distinguishability of two single photons was successfully erased using single photon frequency up-conversion. A frequency nondegenerate photon pair generated via spontaneous four-wave mixing in a dispersion shifted fiber was used to emulate two telecom-band single photons that were in the same temporal mode but in different frequency modes. The frequencies of these photons were converted to the same frequency by using the sum-frequency generation process in periodically poled lithium niobate waveguides, while maintaining their temporal indistinguishability. As a result, the two converted photons exhibited a nonclassical dip in a Hong-Ou-Mandel quantum interference experiment. The present scheme will add flexibility to networking quantum information systems that use photons with various wavelengths.     

Unified Field Theory with EINSTEINian Photons and Heavy Bosons as Field Quants

After discussing in two previous papers [1, 2] the classical electrodynamics which corresponds to the quantum electrodynamics with two sorts of photons (photons with zero rest mass and nonvanishing rest mass), in the present paper the general field theory of a vector field A^v with two sorts if field quanta is given. It is shown that the postulate of the “unity of the four-current” determining the physical contents of this theory makes it possible to regard it as a classical ansatz of a unified theory of the electromagnetic and the weak interactions. From the “unity of the currents” results that the electrons are δ-like point-particles with a finite self-potential and finite field masses M = ε²/2 kc^?2. The COMPTON wave-length of the heavy photons k^?1 = h/mc has the meaning of an “elementary length” for the electromagnetic interactions and the rest mass m = khc^?1 of these bosons is of the order of a baryon mass.