· Web viewTo measure the vibrational transitions within N 2 + Raman spectroscopy will be...
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Search for changes of fundamental constants Supervisors: M. Keller (University of Sussex) (Primary Supervisor) Prof R. Thompson (Imperial College) Background: - The laws of physics are governed by a set of fundamental constants which determine the structure of the universe from sub-atomic particles to large galaxy clusters. Many theories which aim to unify all fundamental forces (weak, strong, and electromagnetic interaction and gravity) and cosmological models predict that fundamental constants change in time. Two particularly interesting constants are the fine structure constant and the proton-to-electron mass ratio . represents the strength of the electromagnetic interaction whereas represents the strong interaction. In recent years changes in have been measured to better than =(1.6±2.3)·10 - 17 /year (assuming a linear change). However, has been measured only to an accuracy of = (0.1±1.3)·10 -16 /year. At the ITCM group at Sussex (primary location of project), we have set up an experiment which aims to measure the proton-to-electron mass ratio with a higher accuracy than currently possible. We employ trapped ions to perform high resolution spectroscopy to determine the frequencies of particular transitions. Vibrational transitions of N 2 + are prime candidates for this - as not only can N 2 + be produced in a specific state, but systematic uncertainties are also very small. Trapping calcium ions alongside the N 2 + ions enables sympathetic laser cooling of the molecules in the trapping potential. Furthermore, the S 1/2 to D 5/2 transition in calcium ions can be utilised as a frequency reference. We operate an ion trap which is combined with a molecular beam line to load nitrogen into the trap together with calcium ions (see figure 1). Nitrogen and calcium ions have been loaded and identified. However, the loading of the N 2 + through photoionisation is currently not entirely state selective. Exploiting methods from quantum information processing the quantum state of the molecular ions is transferred to the calcium ion which in turn can be easily measured through fluorescence detection. In this way a spectroscopic signal can be obtained without destroying the molecule which is beyond the current state-of- the-art. As a frequency reference for the N 2 + -spectroscopy, we are currently preparing a laser system for the spectroscopy of calcium ions with a target linewidth of 1Hz. First Year Project: A prerequisite for the high resolution spectroscopy of N 2 + is the precise loading of molecular ions in a specific internal state into the trap. You will use a pulsed laser system to photoionise N 2 in order to generate molecular ions in a specific state with high yield and state selectivity. In this 6 month project you will use a set-up that generates a molecular beam Figure 1 : Set-up of the experiment with the molecular beam line and an ion trap.
Transcript of · Web viewTo measure the vibrational transitions within N 2 + Raman spectroscopy will be...
Search for changes of fundamental constantsSupervisors: M. Keller (University of Sussex) (Primary Supervisor)
Prof R. Thompson (Imperial College)
Background: - The laws of physics are governed by a set of fundamental constants which determine the structure of the universe from sub-atomic particles to large galaxy clusters. Many theories which aim to unify all fundamental forces (weak, strong, and electromagnetic interaction and gravity) and cosmological models predict that fundamental constants change in time. Two particularly interesting constants are the fine structure constant and the proton-to-electron mass ratio . represents the strength of the electromagnetic interaction whereas represents the strong interaction. In recent years changes in have been measured to better than =(1.6±2.3)·10-17/year (assuming a linear change). However, has been measured only to an accuracy of = (0.1±1.3)·10-16/year.
At the ITCM group at Sussex (primary location of project), we have set up an experiment which aims to measure the proton-to-electron mass ratio with a higher accuracy than currently possible. We employ trapped ions to perform high resolution spectroscopy to determine the frequencies of particular transitions. Vibrational transitions of N2
+ are prime candidates for this - as not only can N2
+ be produced in a specific state, but systematic uncertainties are also very small. Trapping calcium ions alongside the N2
+ ions enables sympathetic laser cooling of the molecules in the trapping potential.
Furthermore, the S1/2 to D5/2 transition in calcium ions can be utilised as a frequency reference.
We operate an ion trap which is combined with a molecular beam line to load nitrogen into the trap together with calcium ions (see figure 1). Nitrogen and calcium ions have been loaded and identified. However, the loading of the N2
+ through photoionisation is currently not entirely state selective. Exploiting methods from quantum information processing the quantum state of the molecular ions is transferred to the calcium ion which in turn can be easily measured through fluorescence detection. In this way a spectroscopic signal can be obtained without destroying the molecule which is beyond the current state-of-the-art. As a frequency reference for the N2
+-spectroscopy, we are currently preparing a laser system for the spectroscopy of calcium ions with a target linewidth of 1Hz.
First Year Project: A prerequisite for the high resolution spectroscopy of N2+ is the precise loading of
molecular ions in a specific internal state into the trap. You will use a pulsed laser system to photoionise N2 in order to generate molecular ions in a specific state with high yield and state selectivity. In this 6 month project you will use a set-up that generates a molecular beam which then will serve as a target for the pulsed laser radiation. The generated ions will then be detected by utilising a channeltron ion detector. By scanning the laser wavelengths, a photoionisation spectrum will be generated which contains information about the state selectivity and the efficiency.
PhD Project: In your PhD project, you will perform quantum logic spectroscopy of molecular nitrogen ions. Based on the experience you have gained in the first year project, you will implement the tested photoionisation scheme into the existing ion trap set-up. This in turn will be used to trap nitrogen ions in a specific internal state alongside calcium ions. By exploiting the mutual coulomb repulsion, the molecular ions are sympathetically cooled by laser cooling the calcium ions. The resulting well localised molecules exhibit negligible Doppler broadening of transitions; crucially important for high resolution spectroscopy.To measure the vibrational transitions within N2
+ Raman spectroscopy will be employed. To this end, the Raman lasers are applied and subsequently the state of the molecule is probed. The state of the molecule is transferred to the calcium ion using techniques from quantum information processing. Using the ions joint motion in the trapping potential, the quantum state of the molecule is transferred to the calcium ion through the phononic quantum bus. This method can also be employed to entangle the quantum state of the molecule and atom to enhance the accuracy.
Figure 1 : Set-up of the experiment with the molecular beam line and an ion trap.
