- Fysik: The exercise is physics-oriented, meaning every process and aspect we are going to see can be explained using concepts of both classical and quantum physics (e.g. wave-particle duality, diffraction, dispersion, single photons, pulsed laser, etc.).
- Matematik: Math is essential in what involves engineering and computer science, and students will need mathematic instruments to analyze the data they collect during the exercise day (Fourier transform, fitting with Gaussian function, etc.).
Hvad går øvelsen ud på?
Would you like to have an insight into how quantum light is generated for future quantum information technologies? Would you like to have hands-on experience on how to manipulate a classical light source for an efficient quantum light generation?
In our lab, you will have the opportunity to do such cool stuff with some of the state-of-the-art facilities, while learning a lot about the field of quantum photonics.
We are working on the development of future quantum computer. Quantum computer is predicted to efficiently solve many tasks, for example the problems within quantum chemistry, that are intractable on the classical computers. In the optical quantum computing, the quantum bits (Qubits) are encoded in the single photons. Therefore, a bright, stable, and on-demand source of indistinguishable single photons is essential to perform efficient optical quantum information processing. In order to generate thousands of highly indistinguishable single photons, we need to develop an advanced optical excitation scheme.
Some of the most recent and advanced excitation schemes rely on a coherent excitation through a pair of slightly detuned laser pulses. Upon absorption of the pulses, the quantum dot is driven to populating its upper energy level, and, eventually, the emission of the single photons can take place.
To generate the two pulses from a single laser pulse that we have in our laboratory, it is necessary to somehow select and filter out only the wavelength that we want. How is it possible to do that? Before answering to this question, we should also mention that the duration of a single laser pulse is of the order of 100fs (1000e-15) and, unfortunately, there is no way of manipulating such fast pulses in the temporal domain relying on some electrical devices.
Hvordan foregår øvelsen?
To singularly address the spectral components of the pulses we need to separate them in the spatial domain. Such result can be achieved thanks to the dispersion of light given by a grating. Dispersion is an optical phenomenon according to which the phase velocity of a wave depends on its frequency.
In the experimental exercise, we will try to understand how a grating works and how can we implement it for the generation of the above-mentioned detuned pulses, which we need to efficiently excite a quantum dot.
To do this, we will first implement a halogen lamp producing a white light featuring a broad spectrum, a diffraction (reflective or refractive) grating, a lens to collect the light in an optical fiber and, ultimately, a spectrometer to check what wavelength we managed to collect. In this way, we can get an idea of how to proceed into the more complex and delicate task of spectrally select very narrow and neighbouring frequencies. What is more, the selected wavelength from the laser which we need is not even visible to the human naked eye!
Believe it or not, the quantum dots will lighten up when we shine them with those two laser pulses even if both of them are at a different frequency than the emitter.
Hvilke faciliteter kommer du til at bruge?
The participant students have the opportunity to enter and work in a state-of-the-art quantum optical lab, equipped with advanced tools such as Femtosecond Laser, Optical Parametric Oscillator, Spectrometer, Single-Photon Detector, Microscope, and many more optics tools.
The data from the exercise will help the student understand the diffraction property of light and how light can be manipulated for better light-matter interaction.
In addition, this exercise will be key for the efficient generation of single photons for quantum information technology applications.
09:00-10:00 Introduction and brief theoretical discussion about what we are going to do and see in the lab
10:00-11:30 First experiment with diffraction grating
11:30-12:30 Lunch (bring your own, or have some money for the canteen)
12:30-14:30 Second experiment with quantum dots
14:30-15:00 Final discussions
Note: This is a tentative program, we might deviate from it if needed.
The final output of the experiment will be given by the optical spectrum of the generated two-pulses, compared to spectrally broad fs-laser. Furthermore, we can also look at the frequency of the light emitted by the single quantum emitters.
All of this is possible thanks to the spectrometer that we have on our optical table (and surprise surprise, the working principle of such spectrometer is based on another diffraction grating!).
The file produced is a specific and dedicated one, however, we can decide to export the data simply as two arrays of numbers in a .txt or .xls: one for the wavelengths and the other for the number of counts for each wavelength.
The students will be able to plot and look at the spectra using simple tools, for instance like the ones provided by Microsoft 365. If anyone is able to play the collected data with Python and Matlab, they’re very welcome to do that.
Forslag til litteratur, du kan bruge i din opgave og som baggrund for øvelsen:
1. Quantum computing with light
2. Making Quantum Light with Quantum Dots
NB: Når du har tilmeldt dig, vil du få besked, hvis der er litteratur, du skal læse som forberedelse til øvelsen.
- Quantum mechanics
- Single Photon Source
- Ultrashort pulse laser
- Diffraction grating
- Spatial Light Modulator