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Quantum Measurement and Manipulation Group

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A long-awaited update!

In the past years, the QMMG group has produced a number of nice publications in both quantum theory, experiment, and education. Head over to the publications page to take a look!

We have also said goodbye to a number of great students whose hard work helps make this group the amazing place that it is.

Our PhD students Jesper and Shaeema both successfully defended their theses!

These years also saw successful master's defenses from Lukas, Jesper A., Thomas, and Tobias. Nikolaj also submitted a successful bachelor's project.

Congratulations to all of these students! We thank them for their years of hard work and wish them the best of luck in what is to come in their bright futures.

Finally, after an unfortunate experimental accident in 2019, we were able to get our single atom signals back! We send our atomic love to everyone reading this page, and you should all be on the lookout for new, great science from our quantum gas microscopy experiment!

A new paper on the ArXiv: Spatial tomography of individual atoms in a quantum gas microscope

Check out our new paper on the preprint server: Spatial tomography of individual atoms in a quantum gas microscope, https://arxiv.org/abs/1912.03079.

We demonstrate a method to determine the position of single atoms in a three-dimensional optical lattice. Atoms are sparsely loaded from a far-off-resonant optical tweezer into a few vertical planes of a cubic optical lattice positioned near a high-resolution microscope objective. In a single realization of the experiment, we pin the atoms in deep lattices and then acquire multiple fluorescence images with single-site resolution. The objective is translated between images, bringing different vertical planes of the lattice into focus. In this way, we tomographically reconstruct the atom distribution in three dimensions. This opens up the possibility of extending the domain of quantum simulation using quantum gas microscopes from two to three dimensions.

(10/12 2019)

A new publication in Journal of Physics B: Spatially-selective in situ magnetometry of ultracold atomic clouds

Our paper, Spatially-selective in situ magnetometry of ultracold atomic clouds, is now published in Journal of Physics B. The paper can be found under the following link: iopscience.iop.org/article/10.1088/1361-6455/ab0bd6.

(5/3 2019)

Paper published in PNAS: Remote optimization of an ultracold atoms experiment by experts and citizen scientists

Our paper on the Alice Challenge and remote optimisation of BECs was finally published in PNAS.

We developed a versatile remote gaming interface that allowed external experts as well as hundreds of citizen scientists all over the world through multiplayer collaboration and in real time to optimize a quantum gas experiment in a lab at Aarhus University. Surprisingly, both teams quickly used the interface to dramatically improve upon the previous best solutions established after months of careful experimental optimization. Comparing domain experts, algorithms and citizen scientists is a first step towards unravelling how humans solve complex, natural science problems.

Read the official press release or the published paper in PNAS.

(14/11 2018)

Carrie joins the group

We are happy to announce that Carrie Ann Weidner will join the experimental team as a postdoctoral researcher for the next two years to come. Previously she did her PhD in the United States under the supervision of Dana Anderson, at JILA in Boulder, Colorado. There she built an atom interferometer in a system of shaken optical lattices. Welcome Carrie!

(6/8 2018)

A new publication in Journal of Physics B: Measurement-enhanced determination of BEC phase transitions

Our paper, Measurement-enhanced determination of BEC phase transitions, is now published in Journal of Physics B. The paper can be found under the following link: https://doi.org/10.1088/1361-6455/aad447.

(6/8 2018)

Jens defends progress report

Our PhD student Jens Schultz Laustsen defended his progress report, Method and systems needed for a Quantum gas microscope, with success. Nils Kjærgaard from the university of Otago, New Zealand came to be an external examiner. Congratulations to Jens, who will now continue working towards the ultimate goal of every PhD student.

(22/6 2018)

Single atom images improved

With the latest progress in the lab on the high resolution imaging, we have been working on cleaning the signal to achieve better signal compared to the background level of noise. The image attached displays some tens of 87Rb atoms, trapped in deep optical lattices, and imaged by capturing fluorescent light emitted when the atoms are exposed to near resonant light.

(19/6 2018)

Single atoms observed, in the shape of a heart

As a result of past several months hard work, we have now achieved a greatly improved signal from single atoms trapped in the optical lattices. Here a heart shaped laser beam is projected into the atomic cloud yielding the atomic heart shape (as also reported on this page in an entry from 1 year ago, on the 31/5 2017). The difference is that now we can easily identify individual atoms, that ate the individual dots present in the image below. This is a big leap towards quality images from our quantum gas microscope.

This is also an opportunity to introduce a colormap for our quantum gas microscope. It goes through four colors, from black to purple to pink to white. Click on the image for an enlarged version.

(25/5 2018)

Revised paper on the ArXiv: Remote optimization of an ultra-cold atoms experiment

A revised edition of our paper on the Alice challenge and remote optimisation of BEC’s, is now available on the ArXiv. The title is: Remote optimization of an ultra-cold atoms experiment by experts and citizen scientists. Please find the pdf here: https://arxiv.org/abs/1709.02230.

(27/3 2018)

Atom clouds moved with the DMD in the lab

We managed recently for the first time in our lab to transport atoms contained in a single atomic tweezer using the dynamic mode of our DMD. We transported a cloud of atoms containing some 100’s of atoms over a distance of 15 µm. In the image attached we see atoms trapped in a 4 by 4 array of optical tweezers, after the corners of the array have been moved outwards by 5 µm.

(15/2 2018)

First observation of a quantum phase transition in the lab

In the past months we have been working on setting up an optical lattice system in the experiment. As a result we have now successfully demonstrated a quantum phase transition for the first time in the Hires lab, when we drove the superfluid to the Mott insulator transition. This is an experiment parallel to the one reported in the classical paper from 2002, when this was first achieved, see https://www.nature.com/articles/415039a.

In the image we see clearly the distinct coherence peaks of a superfluid state, as it is released from the trap and expands in free fall.

(1/11 2017)

Farewell to Romain

With sadness in our hearts we say farewell to the founding PhD student of the Hires lab Romain Müller, who has now served as a postdoc for almost a year. When he arrived to the lab in 2012, it was totally empty. Romains latest construction, the high resolution microscope setup, will be the central tool in our future studies of ultracold quantum systems. Thank you for all your work.

(13/10 2017)

A paper on the ArXiv: Do physicists stop searches too early?

Today, the preprint of our paper on the Alice Challenge and remote optimisation of BEC’s is out on the ArXiv. The pdf can be found here: https://arxiv.org/abs/1709.02230.

(7/9 2017)

A heart shaped atomic cloud

On the 30th of May our experimentalists created a heart shaped atomic cloud in the laboratory. This is achieved using a Digital Micromirror Device (DMD). A laser beam with the shape of a heart is projected into the atomic cloud, and the atoms take the shape of the laser. We send our love out to the cosmos.

(30/5 2017)

Ottó defends progress report

Our PhD student Ottó Elíasson, successfully defended his progress report: Dual port Faraday imaging for local magnetometry in tweezer arrays. Jürgen Appel from the University of Copenhagen served as an opponent. Ottó is now formally in the prestigious group of part B PhD students. Congratulations Ottó.

(23/5 2017)

Jacob Sherson receives Danish Research Communication Award

Jacob Sherson received the Danish Research Communication Award from H.R.H. Crown Princess Mary at the opening of the Danish Science Festival at Experimentarium on April 24th 2017. Read more at ScienceAtHome.org.

(24/4 2017)

The high resolution optics in place

In the months since the end of the Alice we have given our experiment a makeover. Now the high resolution objective for the experiment is in place along with all the optics accompanying it. We hope to see effects of trapping light coming through the objective, on the atoms anytime soon!

(February 2017)

The Alice swarm challenge is on!

The Alice swarm challenge is on! We opened up the to remote access to the experiment through gameplay on the 27th of September. Participate in a real quantum experiment on alice.scienceathome.org.

(27/9 2016)

The Alice Challenge is on!

The Alice team challenge is on! We opened up for remote access to the experiment through gameplay on the 19th of September. Follow on alice.scienceathome.org.

(19/6 2016)

A beautiful BEC transition in the lab

We observed this beautiful BEC transition in the lab on the 16th of September. The BEC is created with the help of a so-called dimple, a very tightly focused laserbeam.

(16/9 2016)

High sensitivity magnetometry in the Hires lab

One of the main research interests of the experimental team is to utilize the atomic Faraday effect to measure properties of our atomic clouds. In recent work we have built a magnetometer capable of measuring magnetic fields to the precision of 2 nT. Taking into the cycle time of the experiment of about 30 s, the sensitivity of our magnetometer amounts to 12 nT/sqrt(Hz).

(August 2016)

Jacob and Aske at NI week in Austin, Texas

Jacob Sherson and Aske Thorsen flew all the way to Austin, Texas to participate in the National Instruments Week at beginning of August 2016, and display the capabilities of our remote experiment interface. See here: youtu.be/tQpSOZvrBAc.

(2/8 2016)

Jens joins the group as a PhD student

Jens Schultz Laustsen joins the group as a PhD on the 1st of August 2016. Jens is familiar to us, as he did his Bachelors project with us last summer. Big welcome to Jens.

(1/8 2016)

Farewell to Mario

We said farewell to our postdoc Mario Napolitano who left on the 31st of July 2016. Thanks for fantastic 2 years, and good luck in future work!

(31/7 2016)

Paper on the ArXiv: Mapping of BEC phase diagrams

On the 11th of July we just submitted a preprint on the ArXiv of our new paper Measurement-enhanced determination of BEC phase diagrams. Find out how to utilize Faraday imaging, to enhance the performance of your ultracold atoms experiment, here: http://arxiv.org/abs/1607.02934.

(11/7 2016)

Making BEC's remotely!

Over the summer, optimal control experts; an experimentalist, and a young student have had remote access to our experiment in order to create as large BECs as possible. Stay tuned for the exciting results.

(Summer 2016)

First observation of Larmor precession in the lab!

We observed Larmor precession of atoms in the lab on the 23rd of June. Our atoms are magnetized, and when they are abruptly exposed to a magnetic field, pointing in a different direction than their magnetization, the start rotating around this external field. This effect can be used to measure magnetic fields very precisely.

(23/6 2016)

Søren Christensen defends masters project

We congratulate our masters student Søren Christensen on fulfillment of his masters degree, with a project entitled Step-by-step Optimization of the Production of Ultra Cold Atoms, defended on the 6th of May 2016. Thank you for your contribution to the understanding of the fundamentals of our experiment, the MOT and the evaporation process.

(6/5 2016)

Our first PhD defends thesis, congrats Romain!

The groups' first PhD student Romain Müller successfully defended his thesis on the 14th of January 2016. Romain has been with us since the dawn of man, and we are happy to announce that he will be staying with us for longer as a postdoc! Congratulations once again.

(14/1 2016)

Jakob Flyger defends Masters project

Jakob Flyger Jørgensen, our Master’s student defended his thesis Generation of arbitrary Potential Landscapes for Ultra Cold Atoms with success on the 8th of January 2016. Thank you for your valuable input to the experiment.

(8/1 2016)

Aske defends Masters project

Aske Thorsen defended his project A modular control system for cold atom experiments on the 9th of October 2015. Aske’s contribution is truly invaluable. As his project he developed from scratch a new and a very flexible control system for the whole experiment entitled Alice. We are also happy to announce that Aske will be staying for longer time to continue the development of the software.

(9/10 2015)

Mark Bason moves on

On the 31st of September 2015 our postdoc for 3 years, Mark Bason left the group, for a new and an exciting position in Nottingham. We thank Mark for his invaluable contribution to the experiment, it wouldn't have been the same without you.

(31/9 2015)

Welcome Ottó

We welcome Ottó Elíasson who joined the team formally as a PhD student on the 1st of September 2015. Ottó is no newbie in the group, and has been around since spring 2014.

(1/9 2015)

Congratulations to Robert

On the 15th of January Robert Heck successfully defended his progress report "Creation of 87Rb Bose-Einstein Condensates in Different Trap Configurations". The external examiner was Jörg Helge Müller from the Niels Bohr Institute. (01/2015)

Congratulations to Mads

On the 14th of January Mads Kock Pedersen successfully defended his master's thesis "Human and measurement-based quantum optimization and game-based education". The external examiner was Niels O. Andersen from the Niels Bohr Institute. (01/2015)

Many-body state engineering using measurements and fixed unitary dynamics

Published in New Journal of Physics

State preparation in high-dimensional Hilbert-spaces does not require control over a system Hamiltonian or over applicable measurement operators: We show how to prepare a desired state or subspace, given a static projection operator onto the desired target that is applied repeatedly at optimised moments in time. Benchmarks against other schemes, performed on random Hamiltonians and on Bose-Hubbard systems, establish the competitiveness of the method.  (11/2014)

Characterization of Bose-Hubbard models with quantum nondemolition measurements

Published in Physical Review A, as editors suggestion!

We propose a scheme for the detection of quantum phase transitions in the one-dimensional (1D) Bose-Hubbard (BH) and 1D Extended Bose-Hubbard (EBH) models, using the nondemolition measurement technique of quantum polarization spectroscopy. We use collective measurements of the effective total angular momentum of a particular spatial mode to characterize the Mott insulator to superfluid phase transition in the BH model and the transition to a density wave state in the EBH model.We extend the application of collective measurements to the ground states at various deformations of a superlattice potential. (10/14)

Interference of two Bose-Einstein Condensates

Recently we have been able to create multiple BECs using a tightly focussed 'dimple' laser beam. The image to the left shows the interference of these two condensates after releasing them from their traps. We are able to change the initial separation of the condensates and observe how the interference fringe spacing changes. (09/2014)

Welcome to Mario

Mario Napolitano joined the group in June 2014 as a post-doc having previously completed his PhD in Morgan Mitchell's group at ICFO. Mario will bring his expertise in Faraday imaging to the QM&M experiment and help set up our optical lattices. (07/14)

First in-situ BEC pictures using Faraday Imaging

We've been able to take 'Faraday pictures' of our BEC held in a crossed dipole trap. Instead of measuring the light absorbed by the cold atoms we detect the polarisation rotation of the imaging light. This method is much less destructive than absorption imaging and should allow us to take multiple images of the same cold cloud or BEC.

The picture is roughly 100 x 160 micrometers; the actual BEC is much smaller!


Time limited optimal dynamics beyond the Quantum Speed Limit

The quantum speed limit sets the minimum time required to transfer a quantum system completely into a given target state. At shorter times the higher operation speed has to be paid with a loss of fidelity. Here we quantify the trade-off between the fidelity and the duration in a system driven by a time-varying control and interpret the result in Hilbert space geometry. Formulating a necessary convergence criterion for Optimal Control (OC) algorithms allows us to implement an algorithm which minimizes the process duration while obtaining a predefined fidelity. http://arxiv.org/abs/1405.6079 (05/2014)

Spin dynamics in a two dimensional quantum gas

Published in Physical Review A, Rapid comm.

We have investigated spin dynamics in a 2D quantum gas. Through spin-changing collisions, two clouds with opposite spin orientations are spontaneously created in a Bose-Einstein condensate. After ballistic expansion, both clouds acquire ring-shaped density distributions with superimposed  angular density modulations. The  density distributions depend on the applied magnetic field and are well explained by a simple Bogoliubov model. We  show that the two clouds are anti-correlated in momentum space. The observed momentum correlations pave the way towards the creation of an atom source with non-local Einstein-Podolsky-Rosen entanglement. (05/2014)

Welcome to Mathieu

Mathieu de Goer from the department of physics of the Ecole Normale Supérieure de Cachan joined our experiment for a summer internship. He will assist in setting up the lattices and with the testing of the non-destructive imaging of ultracold clouds. (04/2014)

Recent article selected for the front page of the PRA website

Our recent paper has been selected to appear on the PRA website as part of their Kaleidoscope feature. This means that it will feature on their front page for around a month. It appears in cycles so catch it if you can!

One- and two-qubit quantum gates using superimposed optical-lattice potentials

Published in PRA

We propose an architecture which allows for the merger of a selected qubit pair in a long-periodicity superlattice structure consisting of two optical lattices with close-lying periodicity. We numerically optimize the gate time and fidelity, including the effects on neighboring atoms and in the presence of experimental sources of error. Furthermore, the superlattice architecture induces a differential hyperfine shift, allowing for single-qubit gates. The fastest possible single-qubit gate times, given a maximal tolerable rotation error on the remaining atoms at various values of the lattice wavelengths, are identified. (03/2014)

First BEC in the new experiment

After a year and a half of hard work we finally have a BEC! Roughly 300k atoms in a hybrid trap geometry. (01/14)

Lundbeck Foundation Fellowship to Jacob Sherson

Jacob Sherson has just been awarded a Lundbeck Foundation Fellowship valued at DKK 10 million. See more details on the official news announcement.   (11/2013)

Welcome to Robert

Robert Heck joined the group in August 2013 as graduate student. Robert will be working on setting up the QM&M experiment. (08/13)

Welcome to Wenzhou

Wenzhou Zhang joined the group in March 2013. He will work on the new experiment as a postdoctoral researcher. Wenzhou previously worked at the Chinese Academy of Sciences on Bose-Fermi mixtures of ultracold atoms. (03/13)

First MOT in the new lab

On the 18th of February, the first MOT was realized in the new High Resolution Experiment. The system consists of a combined 2D and 3D MOT, and it will form the basis for creating BECs in the new experiment. (02/13)

Marie Curie Individual Fellowship

Recently Mark obtained a Marie Curie Fellowship. Mark works as a postdoctoral researcher on setting up the QM&M experiment. Congratulations to Mark! (12/12)

Welcome to Mark

In July Mark Bason joined our group as a postdoctoral researcher. In the coming years he will work on the QM&M experiment. (07/2012)

Welcome to Romain

In May our group was joined by Romain Müller, who will set up the new HiRes experiment. Romain previously worked on cooling of bosonic cesium and fermionic lithium at Heidelberg University. We all look forward to the exciting start of a new experiment. (05/2012)

Aarhus University Research Foundation funds, AU Ideas Center for Community Driven Research (CODER)

We have just been awarded funding for a three-year interdisciplinary center, CODER, within which we will develop online games allowing users of the internet to contribute to solving actual scientific challenges in the field of quantum physics. As a first challenge we will attempt to assist the players in finding new and more efficient solutions for the realization of quantum gates in a quantum computation architecture based on moving atoms in a lattice around in a focussed tweezer of light. (12/11)

Jacob Sherson receives Steno grant

The prestigious Steno grant is awarded by the Free Research Council (Det Frie Forskningsråd) in the Nature and Universe (FNU) division. It is a four year grant and will allow Jacob Sherson to establish a new research activity in the field of cold atomic gases. (12/10)