Atomic Physics Seminar

Feedback loops are central in most classical control procedures. A controller compares the signal measured by a sensor with the target value. It then adjusts an actuator to bring the signal close to the target value. Generalizing this scheme to the quantum world must overcome a fundamental difficulty: the sensor measurement causes a random back-action on the system. I will present how we have been able to continuously operate a quantum feedback loop stabilizing photon number states in a very high finesse Fabry-Perot cavity. Circular Rydberg atoms repeatedly achieve weak quantum non-demolition measurements of the photon number. A classical computer estimates in real-time the density matrix of the field, based on the outcome of these measurements, and taking into account all known experimental imperfections. It then calculates the amplitude of small classical microwave fields injected into the cavity to bring the field into the target state. We have been able to prepare on demand and stabilize Fock states containing from 1 to 4 photons. This achievement opens interesting perspectives for the production and control of non-classical states for quantum information processing.

Host: 
Mark Saffman
Speaker: Clément Sayrin Laboratoire Kastler Brossel, l'Ecole Normale Supérieure

 

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The quantum computing community is making evermore progress towards constructing a fully functional quantum computer. However, none of the many approaches in the different fields of physics have succeeded to date. In the neutral atom quantum computing approach, which uses atoms trapped by light fields as quantum bits (qubits), many of the requirements for a quantum computer (initialization, readout, single-qubit gates) can be met with well-established spectroscopic techniques. The recent accomplishment of two-qubit gates with neutral atoms leaves only one unattained criterion for a quantum computer: The ability to create an addressable array of many qubits.

We will present computational results on a possible solution to this problem. The diffraction pattern formed by laser light incident on a circular aperture exhibits localized bright and dark spots that can be used as atomic dipole traps. An array of such apertures results in a two-dimensional array of dipole traps that can be individually addressed with a laser beam from the third dimension. By exploiting the polarization dependence of these traps, we can also bring traps together and apart to facilitate the performance of two-qubit gates, thus creating a potential candidate for a scalable quantum memory for a neutral atom quantum computer.
Host: 
Saffman
Speaker: Katharina Gillen California Polytechnic State University

 

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5310 Chamberlin
Host: 
Walker
Speaker: Tony Tong Oak Ridge National Laboratory

 

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5280 Chamberlin

Precision of the best molecular spectroscopy is currently orders of magnitude behind atomic ion spectroscopy, owing primarily to challenges in molecular state preparation and readout. Applications of improved molecular spectroscopy would include searches for time-variation of fundamental constants, parity violation studies, and searches for fundamental electric dipole moments. Our group at Northwestern University is developing the necessary tools to perform clock-quality spectroscopy on single trapped molecular ions. We are currently working with species having semi-closed electronic cycling transitions, so that optical pumping into the rotational ground state can be achieved by pulse-shaping of a resonant femtosecond laser. I will also describe a simple readout technique we are developing to map the internal molecular state onto a co-trapped atomic ion, using a pulsed radiation pressure force to excite secular motion.

Host: 
Saffman
Speaker: Brian Odom Northwestern University

 

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5280 Chamberlin
Most neutral atom quantum computing experiments rely on destructive state detection techniques that eject the detected qubits from the trap. These techniques limit the repetition rate of these experiments due to the necessity of reloading a new quantum register for each operation.

We address this problem by developing reusable neutral atom qubits. Individual 87Rb atoms are trapped in an optical lattice and are held for upwards of 300 s. Each atom is prepared in an initial quantum state and the state is subsequently detected with 95% accuracy and with less than a 1% probability of losing it from the trap. The combination of long storage times and lossless state detection could help facilitate the development of faster and more complex quantum operations that will enable future advancements in the field of neutral atom quantum information.
Host: 
Saffman
Speaker: Michael Gibbons Georgia Institute of Technology

 

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Precision measurements in atomic systems serve as powerful probes for studying nuclear structure as well as for testing for possible violation of the discrete symmetries. In the first part of this talk, our measurements of the nuclear charge radii of helium-8 and helium-6 will be discussed. The charge radius measurements of these short-lived neutron-rich isotopes serve to test the most precise nuclear models. In the second half of the presentation, our work towards a search for the permanent electric dipole moment (EDM) of radium-225 will be reviewed. The existence of a non-zero EDM signifies the violation of parity (P) and time-reversal (T) symmetry. Radium-225 is believed to be particularly sensitive to T- and P-odd interactions because of its unique nuclear structure.

Host: 
Thad Walker
Speaker: Ibrahim Sulai Argonne National Lab

 

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5310 Chamberlin
Host: 
Thad Walker
Speaker: Mikkel Andersen University of Otago

 

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Room and Building: 
5280 Chamberlin

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