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| EPSRC Reference: |
EP/D500583/1 |
| Title: |
Laser Cooling of Ca to Bose Einstein condensation |
| Principal Investigator: |
Professor E Riis |
| Other Investigators: |
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| Researcher Co-investigator: |
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| Project Partner: |
| National Physical Laboratory |
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| Department: |
Physics |
| Organisation: |
University of Strathclyde |
| Scheme: |
Standard Research |
| Starts: |
01 February 2006 |
Ends: |
31 July 2009 |
Value (£): |
406,098
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| EPSRC Research Topic Classifications: |
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| EPSRC Industrial Sector Classifications: |
| No relevance to Underpinning Sectors |
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| Related Grants: |
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| Panel History: |
| Panel Date | Panel Name | Outcome |
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27 Apr 2005
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Physics Prioritisation Panel Meeting (Science)
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Announced
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Summary |
Bose-Einstein condensates made by laser cooling and evaporative cooling of atoms are the coldest known substance and are beginning to find a wide range of applications from understanding fluids to precision measurements. Most BoseEinstein condensate to date are based 'one-electron atoms', i.e. the atomic structure is determined by a single electron outside a charged core. This generally leads to an atomic structure ideal for laser cooling but without any particularly narrow spectral lines that would be ideal for precision measurement or optical clocks. On the other hand, the two-electron atoms (such a calcium) offer narrow lines associated with transitions, where an electron spin flips, and are still relatively easy to laser cool.
The narrow transition in atomic calcium is key for the present proposal. It will enable us to laser cool the atoms all the way to Bose-Einstein condensation - something that has not been possible to do with other atoms due to the re-absorption of the light scattered on broader lines. An essential part of this is to trap the atoms in the strong light field of a CO2 laser in order to prevent them from falling under gravity while they are slowly cooled on the narrow line.
The direct laser cooling to condensation is radically different from the traditional approach, which relies on atomic collisions. It will therefore provide new insight into the formation of condensates. The CO2 laser offers a wide choice of geometry for the condensate. We can generate condensates in 1, 2 and 3 dimensional lattices and study the interaction of many independently created condensates when they are allowed to 'see' each other due to quantum mechanical tunnelling through the separating barriers.
The ultimate vision for this work is to use the narrow atomic transition for precision measurements (e.g. an optical clock) in what is known as the Heisenberg limit. That requires the preparation through Bose-Einstein condensation of highly entangled multi-particle states, e.g. N atoms in a superposition of ground and excited states such that if one is found in the ground state then they are all in the ground state or vice versa. With states like this it will be possible to obtain a precision on a measurement, that scales as 1/N (the Heisenberg limit) rather than the 1/sqrt(N) associated with Poissonian statistics. This project will explore and develop a range of technologies for the future realisation of such measurements.
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| Final Report Summary |
Bose-Einstein condensates made by laser cooling and evaporative cooling of atoms are the coldest known substance and are beginning to find a wide range of applications from understanding fluids to precision measurements. Most Bose Einstein condensate to date are based 'one-electron atoms', i.e. the atomic structure is determined by a single electron outside a charged core. This generally leads to an atomic structure ideal for laser cooling but without any particularly narrow spectral lines that would be ideal for precision measurement or optical clocks. On the other hand, the two-electron atoms (such a calcium) offer narrow lines associated with transitions, where an electron spin flips, and are still relatively easy to laser cool.
The narrow transition in atomic calcium was a strong motivation for the present work.
It will enable us to laser cool the atoms all the way to Bose-Einstein condensation - something that has not been possible to do with other atoms due to the re-absorption of the light scattered on broader lines. Within the last few months BEC has been achieved in calcium by a group at PTB using a technique akin to the standard route to BEC in alkali metal systems. Crucial for that work as well as our all optical approach was trapping of the atoms in a far off resonant dipole trap. The original intention had been to use a CO2 laser for this, but well into in the project we became aware that the PTB group had evidence, that there was a severe problem with this wavelength. We therefore turned our attention to a wavelength of 1530 nm, which does not suffer from the problems of the CO2 trap. It also serves the dual purpose of repumping atoms lost from the cooling transition. The main loss channel for the calcium magneto-optic trap is a weak decay into a 3P2 state. We have demonstrated that it is possible to access a significant fraction of these atoms, that are magnetically trapped in the MOT field with a lifetime on the range of 1 sec and repump them back into cooling system.
The project will continue beyond the funding period with a DTA student and a self-funded student as well as through a collaboration with the post-doc, who is moving on to a related project in the Netherlands. The aim will be to demonstrate dipole trapping at 1530 nm and selective repumping of cold atoms from this state.
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| Further Information: |
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| Organisation Website: |
http://www.strath.ac.uk |
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