Abstract Quantum mechanics is a physical theory based on statistical laws and can merely predict probabilities for the measurement outcomes, suggesting that it is an average description. Due to the lack of all the details of microscopic physical objects, only probabilistic predictions can be made for physical phenomena. In this paper, we discuss the root of the probabilistic descriptions in quantum theory by recalling the single photon interference experiments conducted by two commonly used optical interferometric systems: the Mazh–Zehnder interferometer (MZI) and Young’s double-slit system (YDS). Though they are both two-path interference, it is shown that the quantum mechanics can provide deterministic predictions for the measurement outcomes in some special cases by adopting the MZI, while only probabilistic predictions can be provided for the measurement outcomes by adopting the YDS. We hope this work can help to understand the probabilistic nature of quantum mechanics.
Abstract Quantum mechanics is a physical theory based on statistical laws and can merely predict probabilities for the measurement outcomes, suggesting that it is an average description. Due to the lack of all the details of microscopic physical objects, only probabilistic predictions can be made for physical phenomena. In this paper, we discuss the root of the probabilistic descriptions in quantum theory by recalling the single photon interference experiments conducted by two commonly used optical interferometric systems: the Mazh–Zehnder interferometer (MZI) and Young’s double-slit system (YDS). Though they are both two-path interference, it is shown that the quantum mechanics can provide deterministic predictions for the measurement outcomes in some special cases by adopting the MZI, while only probabilistic predictions can be provided for the measurement outcomes by adopting the YDS. We hope this work can help to understand the probabilistic nature of quantum mechanics.
Over the past several decades, single photon-based path interference in double-slit experiment has been well demonstrated for the particle nature of photons satisfying complementarity theory, where the quantum mechanical interpretation of the single photon interference fringe is given by Born rule for complex amplitudes in measurements. Unlike most conventional methods using entangled photon pairs, here, a classical coherent light source is directly applied for the proof of the same self-interference phenomenon. Instead of double slits, we use a Mach-Zehnder interferometer as usual, where the resulting self-interference fringe of coherent single photons is exactly the same as that of the coherent photon ensemble of the laser, demonstrating that the classical coherence based on the wave nature is rooted in the single photon self-interference. This unexpected result seems to contradict our common understanding of decoherence phenomena caused by multi-wave interference among bandwidth distributed photons in coherence optics.
Classically, probability is considered in terms of the number of possible outcomes. For example, a die toss has six possible outcomes and a coin toss, two. Probability calculations make use of probabilities and hence of the total number of possible outcomes. Thus, they are not deterministic calculations which follow “what happens” as in Newtonian mechanics. We suggest that if free particle quantum mechanics is probabilistic, it must also involve the notion of possible outcomes in an experiment and not represent a deterministic approach. We suggest, however, that something interesting applies to quantum mechanics because we have suggested that free particle quantum mechanics arises from the Lorentz invariant A = -Et+px. We note that there exist x,t trajectory points which follow x=vt. We also note, however, that one may introduce the idea of intervals dx, dt (because Newton’s dx→0, dt→0 is an idealization) and that A is unchanged for x,t and x+hbar/p , t+hbar/E. In other words, we suggest that there are intervals with probability about each x,t trajectory point. A trajectory point is associated with deterministic physics, but probability about this point is not. In other words, one has a kind of hybrid probability scheme. Thus, exp(ipx) and exp(-iEt) really represent fluctuation probabilities about a trajectory point x and t. These ranges of possible x and t fluctuations about a trajectory point x,t allow for further probability to occur in certain interactions. We consider two examples. The first is 2-slit interference which involves a deterministic particle moving along a straight line towards a 2-slit mechanism perpendicular to its path. At the 2-slit apparatus, one considers a probabilistic calculation as the uncertainty in x, i.e. dx=hbar/p allows for possible interaction with both slits. This involves considering all possible outcomes (i.e. motion through one slit or the other which is a classical situation), but exp(i p dot r1) and exp(i p dot r2) “sit on top” of these trajectories at the 2-slit apparatus and one has interference of the probabilities linked with each classical possible outcome. Thus, there are two sets of probabilities which are intertwined, the probability range hbar/p for each path and the two possible paths which have equal probability. One must consider the possible outcomes for both sets together. We suggest that a similar analysis applies to the case of 1-D reflection-refraction for x=0 at an n1-n2 index of refraction junction. Thus, we suggest that a deterministic free particle with x=vt may encounter probabilistic interaction situations, such as a two-slit apparatus or an n1-n2 index of refraction junction. These are probabilistic only because there is a probability fluctuation scheme in x associated with each deterministic x point. It is this probability which allows for a second probability to arise due to interaction with the slits or at the 1-D n1-n2 junction. In such a case, one must consider all possible outcomes which means that one does not only consider the exp(ipx) type probabilities, but also those linked with the physical interaction, i.e. two possible paths, one from each slit, or an incident, reflected and refracted photon at x=0 (n1-n2 junction). It is a combination of all possible paths which must be used in calculations. We thus suggest that even though there is a sense of determinism, i..e free particles move as x=vt and these exist in the 2-slit case and the 1-D reflection-refraction case, in a probabilistic calculation one must consider all probabilistic outcomes consistent with these. Thus, quantum mechanical calculations are true probabilistic calculations in the sense that they involve all possible outcomes in an analysis.
Quantum mechanics is a fundamental theory to describe the physics of microscopic objects, but there are still questions whether this theory is complete or not. If the answer to this question is no, axioms could be violated. One of the fundamental axioms of quantum mechanics is Born’s rule, which claims that the description of nature is probabilistic (P(r,t) = |Ψ(r,t)|2). Combined with the quantum mechanical superposition of wavefunctions this results in interference terms, which contain all the possible pairings of the states in the superposition, but does not allow higher-order interference terms with more than two constituents.
A mathematical model for the slit experiments in the heart of quantum mechanics is developed to gain insight into quantum theory. The proposed system-theoretical model is entirely based on commutative mathematics, i.e. convolution, and integral transformations, and starts with spacetime functions with inherent energy-based cause and effect relations of the state-function Ѱ in the complex Hilbert space. The benefits of his approach are as 1-Invariance in time reversal. 2-Deterministic result functions in the model in line with the outcome of slit experiments. 3- Separation of causality and cross-correlations of attained states. 4- Disappearance of a posteriori probability of quantum states. 5- Quantum a priori fixed states after causality interactions have ended, (even) when quanta are (light-years) separated. The model predicts the patterns in the experiments with mathematical functions of the energy distributions. The quantum mechanical counterpart description of the physical reality of slit experiments thus may be considered complete in A. Einstein’s definition. The patterns in double slit experiments are found to be an effect of energy (amplitude-) modulation. An equivalent double-slit pattern can be retrieved from an input modulated 1-slit experiment excluding interference interpretations. The system-theoretical model uses generic properties of quanta and evolves into determinism in quantum mechanics slit experiments. The mathematics in the model handles beables by treatment of momentum p in system theoretical I/O relations of the transformed functions and allows the proposed description by the avoidance of a direct addressing of the individual quanta through variables. The following method yields exact, non-probabilistic results.
We propose a modified single-particle Mach-Zehnder interferometer experiment in which the path length of one arm may change (randomly or systematically) according to the value of an external two-valued variable x, for each passage of a particle through the interferometer. Quantum theory predicts an interference pattern that is independent of the sequence of the values of x. On the other hand, corpuscular models that reproduce the results of quantum optics experiments carried out up to this date show a reduced visibility and a shift of the interference pattern depending on the details of the sequence of the values of x. The key question to be answered in a real laboratory experiment is: Which interference pattern is observed? Despite the general believe that quantum theory might be used to describe all single particle experiments, this is an interesting question to be answered since in the proposed experiment the experimental conditions not only continuously change but they might also have causal effects on the passage of the photons through the interferometer. The proposed experiment can be used to determine to what extent quantum theory provides a description of observed events beyond the usual statistical level.
In this paper we attempt to establish a theory of negative (quasi) probability distributions from fundamental principles and apply it to the study of the double-slit experiment in quantum mechanics. We do so in a way that preserves the main conceptual issues intact but allow for a clearer analysis, by representing the double-slit experiment in terms of the Mach-Zehnder interferometer, and show that the main features of quantum systems relevant to the double-slit are present also in the Mach-Zehnder. This converts the problem from a continuous to a discrete random variable representation. We then show that, for the Mach-Zehnder interferometer, negative probabilities do not exist that are consistent with interference and which-path information, contrary to what Feynman believed. However, consistent with Scully et al.'s experiment, if we reduce the amount of experimental information about the system and rely on counterfactual reasoning, a joint negative probability distribution can be constructed for the Mach-Zehnder experiment.