Details of Grant 

EPSRC Reference:	EP/C545648/1
Title:	Polarisation properties of quantum dots: fundamental aspects and device applications
Principal Investigator:	Tartakovskii, Professor A
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Physics and Astronomy
Organisation:	University of Sheffield
Scheme:	Standard Research (Pre-FEC)
Starts:	01 October 2005	Ends:	30 September 2008	Value (£):	87,836
EPSRC Research Topic Classifications:	Materials Characterisation Quantum Optics & Information
EPSRC Industrial Sector Classifications:	Electronics
Related Grants:
Panel History:	Panel Date Panel Name Outcome 18 Apr 2005 Physics Fellowship Interview Panel Deferred 07 Mar 2005 Physics Fellowships Sifting Panel 2005 Deferred
Summary on Grant Application Form
The proposed programme will focus on achieving control of polarisation of charge carriers and photons in semiconductor quantum dots (QDs) and devices comprising these nano-structures. The experiments will be performed using powerful spectroscopy methods with strong involvement of microscopy, ultra-fast pulsed lasers and novel signal detection techniques.QDs which will be studied in the proposed programme are nanoscale In-rich islands surrounded by GaAs crystal matrix. Charge carriers (electrons and holes) captured from the matrix into a QD become isolated from the environment of a large semiconductor crystal and therefore exhibit a range of novel properties highly beneficial for practical device applications. The proposed research will focus on the properties which will be crucially important to understand/realize the potential of QDs for novel ultra-small memories, quantum computing and totally secure communication protocols (quantum cryptography). All these applications rely on control of polarisation properties of both carriers captured in QDs and light emitted as a result of electron-hole interaction. Very importantly, this control will be based on the in-depth knowledge about the dynamics of carriers and photons during their life-time in the complex structure of a semiconductor device. The program will be divided in two interacting parts:1. Spin-polarisation in QDs: dynamics and depolarisation mechanismsElectrons and holes possess a quantum degree of freedom, spin, which acquires discrete values only (for example +or-1/2 for electrons). Spin-up or spindown states can be used as bits in classical memory devices as well as (through interaction between different electrons and holes) building blocks of a quantum computer, with the latter in theory allowing much faster computational algorithms. Due to the isolation from the environment quantum dots are predicted to have very high stability of spin orientation. The latter can still be lost mainly due to interaction with random spins of nuclei or with vibrations of the crystal lattice at elevated temperature. In this proposal these two interaction mechanisms will be studied in detail and ways to tackle the sensitivity of the stable spin-orientation to temperature will be examined in specially designed dots with strong isolation from the GaAs matrix. I also propose to apply electric field to control the dynamics of spin-polarisation. Finally, the stability of spin-polarisation will be studied in an applied magnetic field, acting as an aligner of electron as well as nuclei spins.2. Fabrication of photonic and electronic devices allowing direct control of polarisation of emitted photons and polarised electron-hole states in QDsSimilarly to isolating electrons in ODs, photons can be confined in a microcavity between dielectric mirrors. In a OD the recombination of an electron-hole pair leads to creation of a single photon which can be efficiently extracted from a dot placed in a microcavity due to the enhancement of a confined optical field. Hence, a microcavity with a QD inside can serve as an efficient source delivering single photons (required for quantum cryptography) on demand. Here I propose to design and fabricate a light source for quantum cryptography based on a novel microcavity structure allowing efficient single-photon emission of defined polarisation. To achieve this I propose a novel design of the photonic cavity, which allows control of polarisation of emitted photons. Control of photon polarisation is extremely important for both phase and polarisation based implementations of quantum cryptography as well as for linear optics quantum computing. Finally, the linear polarisation of OD emission will be controlled independently in a specialty designed diode structure by applying electrical field to manipulate the symmetry of the spatial charge distribution.
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Organisation Website:	http://www.shef.ac.uk