In this section, we shall first present the Heisenberg’s operator approach to the double-slit interference without/with a finite slit width, and then the second-quantization’s creation and annihilation-operator approach for the treatment of the double-slit potential
2.1. Heisenberg’s Operator Approach to Double-Slit Interference with a Negligibly Small Slit Width
According to Heisenberg’s quantum operator formalism [
20,
21,
22], the Hamiltonian of a particle, say an electron in this report interacting with the potential of a double slit is given by
where
is the Dirac delta function. The above potential wall of the double slit represents
, and
vanishes elsewhere. According to Heisenberg’s matrix mechanics formalism, one has
where
Let us examine the trajectory of an electron initially at
before hitting the slit-wall at
. One has the impulsive force
and the impulsive action from the slit-wall is given by
If the potential energy
is much greater than the incident kinetic energy, quantum tunneling is not permissible and the electron is reflected. Therefore, the electron can only pass through the potential wall via the double slits.
The slit gap D is the fundamental length unit, and the fundamental mode has 1/2 wavelength equal to D so that the wave has nodes at the slits. The allowed discrete modes have a frequency as an integer multiple of the fundamental mode. One has the following relations between wavelength
of the fundamental cavity mode, wave vector
, and D as
As an electron passes through either slit, it gains a y-component momentum, proportional to
via absorbing or emitting a cavity quanta with the double-slit potential well, and a quantized field amplitude distribution
and a probability of
, which leads to the same probability distribution for the dot-like interference signal when the electron hits the detector.
The above results indicate that when an electron passes through either slit, it interacts with the double slit and receives a kick, representing a quantized momentum transfer
, from one of the cavity modes. This quantum of energy causes the electron to deflect from its original trajectory. As the deflected electron reaches the screen detector, it induces a dot signal. Each of the discrete multiple-mode force components in Eq. (4) leads to a different dot signal on the screen, and as time evolves with more electron counts, an interference pattern emerges. The amplitude distribution of the n
2-th mode is given by
. This value represents the field strength distribution of the cavity quanta, and its square represents the intensity or probability distribution of the cavity-mode quant. This leads to an interference pattern with an intensity proportional to
. The y-component momentum change after the electron passes through the top slit is given by
Accordingly, one has
where
, and the minimal Heisenberg’s uncertainty principle of
was used. Therefore, one has
From Eqs. (5A) and (5A) the deflected electron angles due to the n-th electron passing through the upper beam or the m-th electron of the lower beam are given by
Because of de Broglie’s duality hypothesis, a quantum particle possesses a dual component which can be represented by a complex-value distribution function, and the probability is the squared magnitude. Accordingly, the overall interference intensity from those upper- and lower-beam electrons is given by
where Eq. (5A) of
is used. Because
, the interference intensity of single electrons from the top and bottom beam is given by
where
or
represents the location of the n-th upper-beam or m-th lower-beam electron’s dot signal on the screen. Upon collecting the intermittent dot signals from arriving single electrons without knowing their trajectories, in the continuum limit of a large N, i.e., when the electron’s wavelength is much shorter than that of the fundamental cavity mode, Eq. (6B) can be reduced to the well-known formula [
23] as
This interpretation provides a more physical picture of how single electrons, neutrons, atoms, or molecules can result in an interference pattern yet induce a dot-like signal on a detector screen.Our mechanism offers a better physical explanation to the quantum interference of single particles. With quantized momentum transfer, one can obtain a better picture of how an electron can be deflected from its initial trajectory. According to our mechanism, a single electron can only pass one of the double slits at a time, there is no need for the counter-intuitive wave splitting, self-interference, and then wave recombination of the wave-packet of the same electron before detection. Furthermore, the Copenhagen interpretation of Schrodinger’s wave-equation approach does not need the unphysical wave function collapse hypothesis. According to our model, interference is caused by non-local interaction between the electron and the double-slit, and the interaction can be described as quantized momentum transfer from the double-slit cavity modes. The amplitude of the n2-th cavity mode is given by , which leads to an interference pattern with an intensity proportional to .
In
Figure 1, we use this schematic diagram for a couble0slit interference setup to elucidate our proposed mechanism, which indicates a single electron can only pass through one of the slits. Such a paradigm shift of quantum interpretation for the double-slit interference does not require the unphysical hypothesis of self-interference and wavefunction collapse during measurement.
We use
Figure 2 to illustrate the resultant interference pattern for double-slit with a negligibly small slit width B, which is identical to the typical standard double-slit interference theory.
2.2. Heisenberg’s Operator Approach to Double-Slit Interference with a Finite Slit Width
Now, let’s consider a more realistic case where both slits have a finite width of B, then the potential becomes
where
, if
and vanishes elsewhere. The corresponding force components are given by
According to the above potential, with
and
defined in Eq, (4A), as a sum over the Fourier series components, it has
where
is the sinc-function defined as
Eq. (7) can be simplified and reduced to Eq (4) as B becomes 0. The overall interference intensity is given by
After accumulating the intermittent dot signals of single electrons without distinguishing their trajectories, in the continuum limit of a large N, i.e., when the wavelength of the fundamental cavity mode is much longer than that of the electron, the above equation can be simplified to the well-known formula [
23] as
Equations (10A–10B) serve as the key formulas for double-slit interference with a finite slit width B. Without invoking the wave theory’s counter-intuitive self-interference or the non-physical wavefunction collapse hypothesis, we re-derived the well-known interference formula which is a special case of our more general expression that predicts finer discrete fringes if the slit gap and the electron’s wavelength become comparable. Incoherence in the electron source or instabilities in the experimental setup—arising from mechanical or thermal fluctuations—can degrade the observed interference pattern.
Figure 3.
Double-slit interference pattern with finite slit width (B = 20 nm). An electron beam with wavelength λ = 5 nm is directed toward a double-slit barrier with slit separation D = 100 nm and slit width B = 20 nm. The resulting interference pattern is recorded on a detector screen located L = 100 μm away. The pattern exhibits modulation by a sinc2 envelope due to the finite slit width, superimposed on the cos2 interference fringes.
Figure 3.
Double-slit interference pattern with finite slit width (B = 20 nm). An electron beam with wavelength λ = 5 nm is directed toward a double-slit barrier with slit separation D = 100 nm and slit width B = 20 nm. The resulting interference pattern is recorded on a detector screen located L = 100 μm away. The pattern exhibits modulation by a sinc2 envelope due to the finite slit width, superimposed on the cos2 interference fringes.
2.3. The Second-Quantization Creation and Annihilation Operator Interpretation of Cavity Modes
In addition to the classical cavity field picture employed above, we now briefly reinterpret the discrete momentum transfer process using the formalism of second quantization. The double-slit cavity structure can be modeled as a set of localized quantized field modes, with the field potential expressed in operator form as
where
,
are the annihilation and creation operators for the nth cavity mode, f
and f
are normalized spatial profiles of mode n in the upper and lower slits respectively, and D is the slit separation. When an electron traverses one slit, it interacts with a single quantized field mode via minimal coupling. The momentum it acquires in the y-direction is proportional to the field amplitude of the selected mode
with
. The probability of such a mode interaction depends on the mode’s overlap with the slit structure, and the relative phase between contributions from the two slits. This leads directly to the interference term
. This term now acquires a natural interpretation: it quantifies the relative phase coherence between two cavity modes of equal index n, centered at each slit and separated by D. It corresponds to the projected Fock state overlap for detecting that cavity mode at the screen. If D/λ
c is such that the cosine term vanishes, then destructive interference prevents the excitation of that mode at the detector.
This second-quantized view provides an operator-level underpinning of the field structure responsible for interference, entirely consistent with the real-space Heisenberg dynamics derived earlier. Importantly, it offers a natural path for generalization to entangled cavities and multi-mode interactions. Such an interaction between a single electron with the cavity mode is causal and non-local because the wave nature of the cavity mode represents the electromagnetic force that is relativistic and causal. Although we use single electrons as an example, double-slit interference has been observed for other single particles, such as photons, atoms, and molecules. The interaction of single particles with a double-slit device is essentially an electromagnetic interaction between the particles and the dielectric slit device. Therefore, the basic underlying physics principle is the same.
We now extend the second-quantized operator formulation to include the effect of finite slit width B. Each slit cavity supports a set of standing wave modes that are confined to the physical width of the slit, and these modes can be described using windowed spatial functions. For slit width B, the mode functions take the form if or vanishes elsewhere.
This extension provides a richer basis for describing diffraction envelopes and modal interactions. The finite width introduces a sinc-like diffraction factor in the resulting momentum distribution
This formula captures the convolution of discrete cavity mode excitation with a continuous angular spectrum. The sinc envelope arises from the finite spatial confinement of the field, while the cosine term reflects coherent phase contributions between the upper and lower slits. This combined operator-based view aligns well with both the physical geometry and experimental interference profiles observed in electron and photon double-slit setups with structured slit boundaries.