'Double-slit' and multiple-path Interference studies from Rb excited and ionized by high-resolution laser radiation.
Lead Research Organisation:
University of Manchester
Department Name: Physics and Astronomy
Abstract
The double-slit experiment using electrons to produce interference at a detector was voted as one of the 5 'most beautiful experiments in physics' by Physics World readers in 2002. Recent experiments in 2013 demonstrated that SINGLE electrons that were detected before the next electron was emitted also produce an interference pattern when the signal builds up over time. This convincingly shows individual electrons have both wave-like & particle-like character, as predicted by Richard Feynman in the early 1960's. Feynman thought such experiments would never be done, however advances in technology since then have now made this possible.
The interference pattern arises since we do not know which slit the electron passes through. We assign a wavefunction to the electron, & the slits then define 2 possible pathways for the wave to travel from source to detector. The wavefronts beyond the slits then recombine at the detector, & the square of their sum gives the probability an electron is detected. If the peak of one wave meets the trough of another, the waves cancel & there is zero probability an electron will be detected at that position. By contrast, if two peaks or two troughs arrive at a point, there is then maximum probability an electron will be detected. An interference pattern is hence produced across the detector, which depends on how the waves recombine at any given point.
In Manchester we recently invented a new type of 'double-slit' experiment in a single atom, where the 'slits' are replaced by atomic states 1 & 2 excited by lasers. The laser beam that excites state 1 also ionizes state 2, whereas the laser exciting state 2 ionizes state 1. There are then 2 pathways to ionization, & we do not know which was taken to produce the detected photoelectron. We again have to add the wavefunctions from each path to determine the outcome, leading to interference. The states (slits) can be turned on or off (effectively opening or closing individual slits) by selectively tuning & detuning the lasers & this allows us to determine the interference pattern.
In the new experiments to be carried out in this proposal we will explore this process in much greater detail, by selecting different excited states & by using different laser polarizations. Our collaborators in Germany theoretically predict this will produce large changes to the ensuing pattern. A further prediction we will explore is that injection of a third laser beam can selectively control the interference. This new idea has no analogy in a conventional double-slit experiment & may find application in other areas where wavefunctions must be manipulated (e.g. quantum computing).
There is no reason why these processes must be confined to single atoms & the second facet of this work will explore how laser excitation & ionization can be applied to arrays of atoms. We will first cool the atoms to close to absolute zero in a magneto-optical trap, before creating a periodic array of excited atoms using a standing-wave laser. The atoms will then be ionized by a second laser, set so that the de Broglie wavelength of the emerging photoelectrons is comparable in size to the dimensions of the array. Interference will once again occur, however now the summation is for waves from ALL sites from which the photoelectrons are born. The resulting yield then depends on both the individual atoms, as well as their position in the array. This is expected to be similar to the effect a diffraction grating has on light, however now the waves are for electrons rather than photons. By altering the properties of the lasers we can 'shape' the grating in different ways, which will change the electron distribution that is produced. Initial models from our collaborators support these ideas & experiments are needed to test & refine the models. This work could find application in electron diffraction studies of surfaces & for controlling the injection of electrons into particle accelerators.
The interference pattern arises since we do not know which slit the electron passes through. We assign a wavefunction to the electron, & the slits then define 2 possible pathways for the wave to travel from source to detector. The wavefronts beyond the slits then recombine at the detector, & the square of their sum gives the probability an electron is detected. If the peak of one wave meets the trough of another, the waves cancel & there is zero probability an electron will be detected at that position. By contrast, if two peaks or two troughs arrive at a point, there is then maximum probability an electron will be detected. An interference pattern is hence produced across the detector, which depends on how the waves recombine at any given point.
In Manchester we recently invented a new type of 'double-slit' experiment in a single atom, where the 'slits' are replaced by atomic states 1 & 2 excited by lasers. The laser beam that excites state 1 also ionizes state 2, whereas the laser exciting state 2 ionizes state 1. There are then 2 pathways to ionization, & we do not know which was taken to produce the detected photoelectron. We again have to add the wavefunctions from each path to determine the outcome, leading to interference. The states (slits) can be turned on or off (effectively opening or closing individual slits) by selectively tuning & detuning the lasers & this allows us to determine the interference pattern.
In the new experiments to be carried out in this proposal we will explore this process in much greater detail, by selecting different excited states & by using different laser polarizations. Our collaborators in Germany theoretically predict this will produce large changes to the ensuing pattern. A further prediction we will explore is that injection of a third laser beam can selectively control the interference. This new idea has no analogy in a conventional double-slit experiment & may find application in other areas where wavefunctions must be manipulated (e.g. quantum computing).
There is no reason why these processes must be confined to single atoms & the second facet of this work will explore how laser excitation & ionization can be applied to arrays of atoms. We will first cool the atoms to close to absolute zero in a magneto-optical trap, before creating a periodic array of excited atoms using a standing-wave laser. The atoms will then be ionized by a second laser, set so that the de Broglie wavelength of the emerging photoelectrons is comparable in size to the dimensions of the array. Interference will once again occur, however now the summation is for waves from ALL sites from which the photoelectrons are born. The resulting yield then depends on both the individual atoms, as well as their position in the array. This is expected to be similar to the effect a diffraction grating has on light, however now the waves are for electrons rather than photons. By altering the properties of the lasers we can 'shape' the grating in different ways, which will change the electron distribution that is produced. Initial models from our collaborators support these ideas & experiments are needed to test & refine the models. This work could find application in electron diffraction studies of surfaces & for controlling the injection of electrons into particle accelerators.
People |
ORCID iD |
Andrew Murray (Principal Investigator) |
Publications
Murray A
(2023)
An undergraduate physics experiment to measure the frequency-dependent impedance of inductors using an Anderson bridge
in American Journal of Physics
Murray A
(2023)
Measurements of the Kr ( e , 2 e ) differential cross section in the perpendicular plane from 2 to 120 eV above the ionization threshold
in Physical Review A
Patel M
(2022)
Laser-atom interaction simulator derived from quantum electrodynamics
in Physical Review A
Rogers J
(2022)
A low-cost and reliable laser shutter interlock using a software-command interface
in Measurement Science and Technology
Udommai P
(2021)
Digitally controlled laser frequency stabilization for a ring laser using saturated absorption
in Review of Scientific Instruments
Title | Millennia Pro Interlock custom PCB files |
Description | The schematic, PCB layout and associated libraries for the custom board fabricated for the Millennia Pro interlock box. The files were created in Altium Designer 21 but a Gerber version is included and a ready-to-fabricate version is available at https://oshpark.com/shared_projects/TsGSmbmI. |
Type Of Art | Film/Video/Animation |
Year Produced | 2022 |
URL | https://figshare.manchester.ac.uk/articles/media/Millennia_Pro_Interlock_custom_PCB_files/20037185 |
Title | calculation of density matrix evolution for general states of a system |
Description | This work developed a new general way to calculate the equations of motion for any atomic system coupled by a CW laser. The programme is general and calculates the equations for any system and then solves them using python. It can also generate the equations for input into papers. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2022 |
Provided To Others? | Yes |
Impact | This is a general solver for the QED equations used in laser atom interactions and so is useful for any researchers who wish to calculate the dynamics of their systems. |
URL | https://github.com/mvpmanish/LASED |
Title | laser shutter mechanism for CW lasers using an Arduino |
Description | A new laser shutter has been developed to allow the essential Health and Safety requirements in the laser lab to be fully complied with. The shutter automatically shuts down the laser beam without turning off the lasers (as was done previously with the associated loss of data) by controlling a shutter mechanism. This was developed at a fraction of the cost of commercial systems and has been adopted in different areas within the research institute. |
Type Of Material | Improvements to research infrastructure |
Year Produced | 2022 |
Provided To Others? | Yes |
Impact | This allows data collection without turning off the laser systems, thereby ensuring that we do not lose data. |
Description | Collaboration with theoretical group in Halle, Germany |
Organisation | Martin Luther University of Halle-Wittenberg |
Country | Germany |
Sector | Academic/University |
PI Contribution | A new collaboration has been setup with the group of professor Jamal Berakdar in Halle, Germany to study further the interactions of laser radiation with atoms leading to excitation & ionization. |
Collaborator Contribution | This collaboration has added theoretical calculations to experiments we carried out to look at a new type of double slit experiment in a single atom, which has lead to a Physical Review Letter publication in 2019. |
Impact | Physical Review Letter published February 2019. Further work is ongoing, through which we expect a second paper to be submitted soon. |
Start Year | 2017 |
Description | collaboration with Dr Harvey & Dr Hussey for 3D metal printing |
Organisation | Wayland Additive |
Country | United Kingdom |
Sector | Private |
PI Contribution | Since Dr Harvey left the group and started working for the company Wayland additive we have had a small informal collaboration with him and Dr Martyn Hussey (also an ex-PDRA and PhD student) who are working on the development of 3D metal printing processes for a private company. This collaboration is small, and principally involves discussions about the process as well as ocassionally helping with components for testing. |
Collaborator Contribution | This involves mostly discussions every 2 weeks about how the project is progressing. |
Impact | None so far. |
Start Year | 2021 |
Title | Millennia Pro Interlock ESP32 code |
Description | The code that runs on the ESP32 chip to control the logic of the Millennia Pro pump laser interlock |
Type Of Technology | Software |
Year Produced | 2022 |
Impact | this allows the laser system to operate without having to switch off the pump lasers |
URL | https://figshare.manchester.ac.uk/articles/software/Millennia_Pro_Interlock_ESP32_code/20037176 |