Synopsis

Experiments run in two sessions during Michaelmas (E1a/E1b) and two during Lent (E2a/E2b).  Efforts are made to give students maximum choice and flexibility although it is not always feasible to run all the experiments.

Two weeks is allowed for practical work with a further 9 days for writing the report.  Prior to starting experimental work, students will be given a short briefing from the head of class. They are then expected to work independently, and can carry out experimental work any time when the Part II labs are open 09:00-17:45 (09:00-17:15 Wednesday), during the two week period allowed for practical work.

Experimental Reports

The experimental report should usually be presented in the style of a paper published in a scientific journal. The main text (excluding appendices and abstract) should be concise, 3000 words maximum (excluding references and figure captions). The text should describe and explain the main features of the project, the methods used, results, discussion and conclusions, and should be properly referenced. In addition, there must be an abstract of at most 300 words. Students should refer to the handout ‘Keeping Laboratory Notes and Writing Formal Reports’ for further details about writing experimental reports.

Submission of your report

Upload you report to the TIS. To submit your report, go to the 'My experiments' tab, you will find details on how to submit your work there. You may upload as may copies as you wish up to the deadline. In order to preserve anonymity when your report is looked at by the Part II examiners, your name must not appear on the report itself, but please include the name of the experiment and Head of Class.  

Late Submission of Coursework

The Department of Physics expects students to meet the advertised deadlines for the submission of all coursework, to ensure fairness to all students taking the course and allow prompt marking by the Department. 

In accordance with the University's regulations, work submitted after the advertised deadline will not count towards your final examination mark, unless the Department grants an extension of time on the grounds that there are significant mitigating circumstances.

Students must complete the form available from the teaching webpages, including supporting cases from Tutor and Director of Studies.

In such circumstances, you should submit the work as soon as possible after the deadline.

Before the end of the relevant term, the report will be assessed by the Head of Class, who will then conduct a viva voce examination (typically 30 minutes long). The student will be asked to give a short verbal summary (typically 10 minutes), normally uninterrupted, of the report during the examination. Students should expect to be contacted by the Head of Class shortly after the submission of their report, to arrange the examination.

These Head of Class will write a report to the Part II Examiners and will recommend a mark. These marks are not necessarily final and may be amended by the examiners, who will also look at the report and the Head of Class’s written assessments. After the viva, you will receive a copy of the mark sheet, which will provide feedback on your performance. The marks allocated by the Head of Class are subject to moderation and scaling by the examiners, so the mark you receive may not match the final mark for this piece of work in the College Markbook.

The following guidelines for allocation of marks to Part II experimental reports will be given to the Head of Class.

• Understanding: (30%): of the physical system being measured, and of the experimental design.
• The experiment (40%): how well the work was done, quality of results, discussion of errors.
• Communications skills 1 - Report (20%): Was the report well written and clearly organised, with clear and well balanced arguments, appropriate use of figures, tables and references.
• Communications skills 2 - Viva (10%): Was the student able to summarise the work and respond coherently to questions?

If there are any queries concerning these arrangements, contact, Helen Marshall in the Undergraduate Office (undergraduate-office@phy.cam.ac.uk).

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Optical Pumping of Rb - Dr Christoph Eigen

Part II Laboratory, Room 169 (4 spaces)

The Zeeman effect in the ground state of the rubidium atom is studied by exploiting optical pumping to realize a non-equilibrium population across hyperfine spin states, and then driving radio-frequency (RF) transitions between the hyperfine states (looking at both the steady-state response and the transients when turning on/off the RF).

The objectives of the experiment are:
i) to study the Zeeman effect in the ground state of both isotopes of rubidium (85Rb and 87Rb)
ii) to obtain the nuclear spins of both isotopes, and make accurate measurements of the ground-state Landé g-factors
iii) to use the atoms to measure the Earth’s magnetic field
iv) to observe Rabi oscillations between hyperfine states and study the transients
v) to investigate power broadening in the system
vi) to explore (a) multiphoton absorption and/or (b) moderate magnetic fields where the Zeeman shifts are nonlinear (Breit-Rabi)

The Rb sample is contained in a temperature-controlled cell and coils provide a B-field that both cancels the earth’s field and produces the Zeeman splitting.  Optical pumping by a separate Rb lamp (selecting D1 light with a filter and controlling the polarization with a waveplate) is used to produce a non-equilibrium population of hyperfine states in the Rb atoms. Changes in the absorption of the D1 light can be produced and detected by applying an RF field at the frequency corresponding to the Zeeman splitting.

The experimental apparatus is produced by TeachSpin, and a detailed overview of the underlying physics and technical aspects can be found at: https://www.teachspin.com/optical-pumping. 

The experiment will certainly enhance your understanding of atomic physics! It also lays the foundation for concepts at the heart of the emerging quantum technologies.

Semiconductor Quantum Devices - Dr Adrian Ioenscu

Part II Laboratory, Room 170 (5 spaces)

The resonant tunnelling of electrons in semiconductors  is investigated at both room temperature and 77K.

The experiment involves measurements of a Resonant Tunnelling Diode (RTD), samples of which are manufactured in the Cavendish.  The device acts as a double quantum barrier, the properties of which are an extension of those of the single barrier (met in IB Quantum) and the Fabry-Perot interferometer (IB Optics).

The experiment is designed to be ‘open-ended’ based on measurements of the current/voltage characteristic of the device at both room temperature and 77 K (liquid N2).   The results are compared with the relevant theory.

Mobility of Carriers in Semiconductors - Dr Akshay Rao

Pt II Laboratory, Room 173  (3 spaces)

Propagation of carriers through a semiconductor is measured by a direct method

The purpose of the experiment is to investigate experimentally fundamental transport processes in semiconductors, including drift, diffusion, recombination as well as injection from metal contacts. A pulse of minority carriers is injected at one end of a bar of germanium.  By measuring the arrival time and the shape of the current pulse at the other end of the bar direct information about the charge transport processes in the semiconductor is obtained.

The measurements required include:

i) Measurement of the mobility of Ge and its temperature dependence

ii) Estimate of the minority carrier lifetime in Ge

iii) Verification of the Einstein relation between mobility and diffusion coefficient

iii) Determination of the current/voltage characteristic of the rectifying injecting point contact. 

Phase- Locked loops - Dr Andy Irvine

Bragg Building, Room 169 (3 spaces)

Operation and optimisation of phase-locked loops is investigated, for frequency locking and for recovery of signals buried in noise, and elements of programming-based computer control and data acquisition are introduced.

The experiment is based around the 4046 CMOS integrated circuit; this is designed for phase-locked loop applications and can be operated in two different modes, depending on the type of (integral) phase comparator which is used. The object of the experiment is to investigate the behaviour of the device in a variety of different applications, using each of the available comparators.

The project involves constructing automated control and measurement systems using the graphical LabVIEW programming environment. Control voltages are applied using an Arduino microcontroller (or otherwise) and experimental parameters are measured using a LabVIEW-linked Picoscope. Investigators will:

• Characterise the properties of the two comparator circuits and of the on-board oscillator using an Arduino as a phase-shifting pulse generator and voltage source.
• Measure the stability and locking/capture ranges of the closed-loop system, using the appropriate degree of automation.
• Assemble and investigate the behaviour of the phase-locked loop in some typical applications – as a frequency multiplier, a demodulator of frequency-modulated signals as a clock regenerator for an irregular train of pulses.

An ability to assemble working circuits and a basic understanding of electronics are helpful assets when doing the experiment. Very basic coding experience will help, though this is not a programming project and will be perfectly accessible to non-experts.

Pulsed NMR at 15 MHz – Prof. Sian Dutton

Part II Laboratory, Room 170 (8 spaces)

This experiment investigates and demonstrates the principles of Nuclear Magnetic Resonance (NMR).  Spin-echo methods are employed to study the characteristic NMR properties of a number of samples.

Particle Tracks - Dr Paula Alvarez Cartelle

Bragg Building, Room 163 (5 spaces)

Properties of short-lived hyperons are measured by analysing photographs from a liquid hydrogen bubble chamber

The experiment is based around measurements of film taken from bubble chamber experiments at the CERN particle physics laboratory near Geneva. While this technique is no longer current, it provides an immediate visual, introduction to the subject.

Interactions of  K-  and protons p, in which hyperons are produced, are studied.
Measurements of the decay of  product S+ and S- hyperons are made using the projected length of the hyperon track and the curvature of the track of the recoil pion and, in the case of the S+ hyperon the decay mode (via proton or neutron) is noted.   The decays of neutral hyperons are also studied.

Quantities which you are asked to measure include:

(i) the masses and mean lives of S+ and S- hyperons

(ii) the branching ratios for the decays of the S+.

(iii) the mass and mean life of the neutral hyperon.

Scanning Tunnelling Microscopy - Dr David Ward

Pt IB Laboratory, Room 166 (4 spaces)

The growth kinetics of graphite oxidation pits are investigated on atomic length scales

The Scanning Tunnelling Microscope (STM) is an important tool in current research as it is capable of mapping surfaces on an atomic scale.  Its operation makes use of the tunnelling current of electrons between an atomically sharp tip and a surface placed a very short distance (~10 Å) away.

The instrument is interfaced to, and controlled by, a computer which also produces the images. 

In this experiment, the STM is used to examine the surface of a graphite crystal. Measurements are made on different scales in order to become familiar with, and illustrate the potential of, the instrument.  The STM is then used to investigate the nucleation and growth of oxidation pits on the surface of the graphite.

Coherence and information in a fibre interferometer - Dr Tijmen Euser

Part II Laboratory, Room 167 (3 spaces)

In this practical we consider a Mach Zehnder (MZ) interferometer and some quantum-mechanical implications. The pattern observed behind an MZ interferometer shows interference fringes, provided there is no way to determine which arm a photon has passed. Here we will place an optical amplifier along one of the MZ arms. The amplifier increases via stimulated emission the intensity of laser pulses. When coherent photon pulses from a laser pass the arm, they stimulate the emission of identical, coherent photons by the atoms of the amplifier medium.

What is the outcome of this experiment: Does the amplification localize the photons in one arm and is the interference therefore suppressed? Or does the process of stimulated emission not constrain the position of the incoming photons, so that the interference pattern is preserved and even amplified through the contribution of the stimulated emissions?

The aim of the practical is to perform the measurements and to explain the results. Some of the intermediate objectives are:

(i)  To build a Mach-Zehnder interferometer and to characterize the interference patterns obtained for different light sources.
(ii)  To study optical amplification and to understand how the gain and noise of an amplifier are determined by stimulated and spontaneous emission processes.
 (iii) To place an optical amplifier in one arm of a Mach-Zehnder interferometer and to explain the results.