First Demonstration of Antimatter Quantum Interferometry

TL;DR

This paper reports the first experimental demonstration of antimatter-wave interference using single-positrons, providing crucial evidence for quantum interference phenomena in antimatter.

Contribution

It presents the first experimental evidence of antimatter-wave interference, extending quantum interference studies to antimatter particles.

Findings

First demonstration of antimatter quantum interference

Evidence supporting quantum behavior of antimatter

Advancement in antimatter wave research

Abstract

This paper descrives the first experimental evidence of antimatter-wave interference, a process at the heart of Quantum Physics and its interpretation. For the case of ordinary matter particles, interference phenomena have been observed in a variety of cases, ranging to electrons up to complex molecules. Here I present the first demonstration of single-positrons quantum interference.

Equations

$$\frac{L_1}{L_2}=\frac{d_1}{d_2}-1$$

Full text

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1 Introduction

The concept of wave-particle duality was introduced in 1923 by de Broglie[1, 2]: the Planck constant $h$ relates the momentum of a massive particle $p$ to a waveleght $\lambda_{dB}=h/p$.

Accordingly, diffraction and interference phenomena have been observed for a variety of particles, ranging from electrons[3, 4], to neutrons[5, 6], and complex molecules[7, 8, 9]. Gravitationally induced phase shifts were measured with neutrons in the famous Colella-Overhauser-Werner series of experiments[10, 11].

The experimental study of single particle (one-at-a-time) double-slit interference was proposed by Feynman as a gedanken experiment and a decisive test that has in it the heart of quantum mechanics[12].

The single electron interference experiment was made for the first time in 1976[13] and subsequently voted ”the most beautiful experiment” by the readers of the Physics World magazine[14]. A few years later, diffraction by positrons was observed for the first time[15]. A demonstration of single-particle interference for any antimatter particle was however still missing.

In order to fill this gap, we have designed, realized and operated a Talbot-Lau interferometer[16] suitable for anti-electrons (positrons) in the 5-18 keV energy range. This development is part of the QUPLAS (QUantum interferometry and gravitation with Positrons and LASers) research program[17, 18, 19, 20].

2 The setup

The experiment is located at the variable energy positron beam facility of L-NESS (Laboratory for Nanostructure Epitaxy and Spintronics on Silicon) of the Politecnico di Milano in Como (Italy). The positron beam has an intensity of $\sim 5\times 10^{3}$ $e^{+}/s$, an energy between 5 and 18 keV (resolution better than 0.1%) and an angular divergence of a few milliradians, producing a typical spot of about 2 $mm$. The beam is collimated and followed by the interferometer and the emulsion detector as shown in fig. 1. The interferometer structure consists of two gratings in a period-magnifying Talbot-Lau configuration[18]. The two gold-coated SiN gratings (11.8 $cm$ apart) have nominal periods of d1=1.2 and d2=1 $\mu m$ respectively and a 50% open fraction, producing a d3=5.9 $\mu m$ period fringes at the location of the emulsion detector.

The periodic spatial distribution is recorded by the emulsion detector that has a $\sim\mu m$ resolution. The emulsion has been tested at the QUPLAS energies in a dedicated ”engineering” run[20] and the setup has been aligned and calibrated as described in [21].

The positron flux ($\sim 10^{3}/s$) is produced by an incoherent (radioactive) source. Since the transit time of the particles in the interferometer is of $\sim 10^{-8}$ $s$, QUPLAS is clearly a one-particle-at-a-time experiment.

3 Results

The configuration of the interferometer was meeting the resonant condition for the nominal 14 keV energy value, as[18]

[TABLE]

Exposures of the emulsions were made at 8, 9, 11, 14 and 16 keV positron energies; the results are presented in fig. 2. For each energy, the emulsion was exposed for about 100 hours, then developed and the impact positions of positrons were digitized. The analysis strategy was to fit the fringes distribution as a function of both the period and the rotation angle between the interferometer and the emulsion detector (the remaining important alignment parameter). Periodical patterns as the one shown in the insert of fig. 2 has been obtained, with the expected periodicity of 5.9 $\mu m$.

4 Discussion

After having shown periodical patterns as expected, in order to fully prove the quantum nature of the effect, the visibility was studied as a function of the energy (wavelength). As shown in fig. 3, the fringes contrast as a function of energy disagrees with projective classical mechanics and is in agreement with the quantum mechanical model of the system[17, 18].

This is the first demonstration of antimatter quantum interference.