The projectIn September 2009, our research group created the first strontium Bose-Einstein condensate (BEC) in the world. Now we are exploring the exciting new fields of research opened up by this break-through. Strontium is an alkaline-earth element and has two electrons in its outer shell. This gives it many unique properties not existing in conventional alkali systems. Those comprise a ground state free of electronic magnetic moment, the existence of metastable states, and optical transitions with small linewidth. These properties have been used since a few years to built optical clocks and are at the heart of recent proposals in fields as diverse as the variation of fundamental constants, mHz linewidth lasers, and quantum simulation and computation. Our goal is to create and investigate novel quantum systems that are beyond the reach of alkali quantum gases. The guiding topics of our research will be quantum computation and quantum simulation of many-body systems. The fundamental idea behind quantum computation with Sr is that the fermionic isotope 87Sr has a nuclear spin, which can be used to store quantum information in a well-protected way. At the same time, the complex electronic structure of Sr allows to manipulate the information. The interest in quantum simulation of lattice many-body systems comes from the fact that those systems are very difficult or even impossible to describe using classical computers. Even very fundamental and relevant models have not yet been solved. A quantum simulator is a special task quantum computer that emulates the physics of the system of interest. Cold atom systems can serve as quantum simulators since they are very well controlled. Strontium with its unique properties enables the simulation of systems not accessible with the simpler alkali atoms used so far. We will also study mixtures of strontium with rubidium with the goal to create SrRb ground state molecules. Heteronuclear bi-alkali ground state molecules possess a permanent electric dipole moment, which gives rise to directional, long-range interactions. They are currently a hot topic and have just recently been produced for the first time. The difference between bi-alkali and alkali/alkaline-earth ground state molecules is that the latter possess an outer shell electron. This provides them with a magnetic dipole moment in addition to the electric dipole moment. The properties of the molecules can thus be tuned with electric and magnetic fields. This can for example be used to engineer spin-dependent, tunable, long-range interactions, which can be used for quantum simulation. These research avenues for quantum-degenerate strontium gases are very rich and promise new insights into physics ranging from molecules over novel quantum computation approaches to quantum many-body systems.
The achievementsBose-Einstein Condensation of Strontium
In September 2009, just 17 months after starting the project in an empty lab, we were the first to attain Bose-Einstein condensation strontium. We used the 84Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. We obtained pure condensates containing 1.5 x 105 atoms, which puts 84Sr in a prime position for future experiments on quantum-degenerate gases of atomic two-electron systems.
The phase-transition from a thermal sample to a pure BEC of 84Sr.
Double-degenerate Bose-Fermi Mixture of Strontium
87Sr is the only fermionic isotope of strontium and the only isotope possessing a nuclear spin, which is at the heart of nearly all schemes of quantum computation and simulation with strontium. We have prepared 87Sr in a single internal state and cooled it to quantum degeneracy using 84Sr.
A pure BEC of 84Sr and a Fermi sea of 87Sr 15 ms after release from the trap.
Bose-Einstein condensation of 86Sr 86Sr has a large scattering length of +800 Bohr, leading to strong three-body loss. We show that it is all the same possible to perform evaporative cooling and obtain a BEC.
Evaporative cooling from a thermal sample to a pure BEC of 86Sr.
Detection and manipulation of nuclear spin states in fermionic strontium 87Sr has a large nuclear spin, which has many applications in quantum simulation and computation. We detect and manipulate the spin-state distribution, as required for those applications.
The ten mF states of 87Sr after optical Stern-Gerlach state separation.
Mott-insulator of 84SrWe have observed the superfluid to Mott-insulator transition with 84Sr, by loading a BEC into an optical lattice. In quantum simulations, the optical lattice simulates the crystaline lattice of a solid.
The superfluid to Mott-insulator transition (click image to enlarge). A BEC (left, back) is subjected to an optical lattice of increasing depth. For small lattice depths, diffraction peaks appear. For large depths, the Mott-insulater phase is reached: atoms are localized on lattice sites and coherence is lost (front). The process is adiabatic and a BEC reappears when reducing the lattice depth again (right, back). The lab
The vacuum chamber in which the experiments take place, surrounded by magnetic field coils and optics.
The heart of the apparatus, a glass cell vacuum chamber, surrounded by magnetic field coils and optics. The blue fluorescence of a 88Sr magneto-optical trap is visible as reflection in the glass cell. The team
The team in November 2011 (from left to right):
The team in May 2011 (from left to right):
The team in September 2009 (from left to right):
Open positionsWe have open positions for diploma/master students, PhD students and postdocs. Please contact Florian Schreck for information. References
Further reading
FundingThe project is hosted by the Austrian Academy of Sciences at the Institute for Quantumoptics and Quantuminformation. Funding is provided by a START prize of the FWF and the BMWF and the iSense FET-Open grant of the European Commission.
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| last change: 11-08-16 by FS |
