Demonstration of the Jaynes-Cummings ladder with Rydberg-dressed atoms


Demonstration of the Jaynes-Cummings ladder with Rydberg-dressed atoms

Jongmin Lee, Michael J. Martin, Yuan-Yu Jau, Tyler Keating, Ivan H. Deutsch, and Grant Biedermann

The Jaynes-Cummings model, a widely employed theoretical framework in cavity quantum electrodynamics, is experimentally tested on a platform involving Rydberg-blockaded atomic ensembles. The work opens the way to a richer exploration of protocols for quantum control or, more broadly, quantum computing.

The full article is available online at Phys. Rev. A 95, 041801(R) (2017)


FIG 1.  Experimental setup.  The Rydberg laser and the Raman lasers are  aligned along the x axis.  Two optical tweezers are formed by two lasers  with an angular separation θ..  In this setup, eight electrodes control the electric fields near the trapped atoms.  The bias magnetic field is applied along the x axis.



Quantum Computation from Symmetric Quantum Matter

Jacob Miller and Akimasa Miyake have recently published a paper in Nature Partner Journal Quantum Information showing that quantum computers with distinct operational advantages can be built using a form of symmetric topological matter. Their work deals with measurement-based quantum computation (MQC), a way of powering computation with only single-spin measurements and a large entangled quantum “resource” state. MQC is a natural way to study the connection between different forms of quantum topological order, the types of quantum computation they can power, and what measurements are needed for this computation.

The authors show that two complementary forms of symmetric topological order are particularly useful for quantum computation. While previous resource states have only utilized the first form, a new Union Jack state is constructed to study the second, stronger form. While both are sufficient to achieve any desired computation, the quantum order found in the Union Jack state can achieve this using simpler measurements, pointing towards a surprising new resource for simplifying quantum computation.

The full article is available online at


Do I smell percolation?
(Left) The Union Jack state, a new state with a strong form of symmetric quantum order which makes it useful for quantum computation. (Right) One step in the procedure for computing with the Union Jack state. Measurements on half of the sites drive the system through a quantum phase transition, which leads to a computationally useful graph state being randomly condensed on the unmeasured spins.


Integrated quantum information processing in the dispersive regime with fewer atoms

Nanofiber Scheme
The integration of nanophotonics with ultracold atoms opens the door to new protocols in quantum information processing. Strong entangling interactions between atoms and photons are the key ingredient. Whereas a resonant interaction can lead to the strongest entanglement per atom, this requires special geometries that limit decoherence. Off-resonant dispersive interactions, where a phase shift is associated with the atom-photon interaction, provides an alternative route to strong entanglement. This can be achieved due to the “cooperativity” of a large ensemble of atoms that can be homogeneously trapped in the evanescent field of an optical nanofiber using well-known techniques (see figure above). The optical scattering cross section closely matches the guided beam mode area across the entire length of the nanofiber. Our recent paper pedagogically develops the theory to describe how the light dispersively responds to an ensemble of atoms in the optical nanofiber waveguide platform and how this can yield large cooperativity. As an application of the theory, we study the creation of spin squeezed states for application in improved precision of atomic clocks. With only a few thousand Cesium atoms, a nontrivial squeezed state can be created using an anisotropic property of the nanofiber modes, which is not available or hard to implement in free space. This is a first step towards more general protocols involving the production of nonGaussian atomic states and their interaction with nonclassical light.


Comments and discussions can go to its Github repository.


Xiaodong Qi, Ben Q. Baragiola, Poul S. Jessen, and Ivan H. Deutsch, Dispersive response of atoms trapped near the surface of an optical nanofiber with applications to quantum nondemolition measurement and spin squeezing, Phys. Rev. A 93, 023817 (2016). [PDF]

Thermodynamics with Correlations: Enhancing the Performance of Quantum Maxwell Demons

Adrian Chapman and Akimasa Miyake have recently published their paper in Physical Review E, demonstrating that a Maxwell demon can exploit correlations in its memory to enhance its thermodynamic performance over the demon which cannot. In this classic thought experiment, the demon uses information, rather than energy, to perform a thermodynamic task such as refrigeration. One example is realized by a demon who controls the door of a bipartite container filled with gas. Using a microscopic measuring device, the demon allows only faster molecules to one side while allowing only slower molecules to the other, apparently performing cooling for free. Only when one accounts for the inevitable energy cost of erasing the device’s memory does one see that this supposed perpetual motion machine is actually a refrigerator. This fact suggests that information has value in thermodynamics.

In their paper, the authors consider a simple concrete model of physical system, which acts as an autonomous Maxwell demon. In many previous models, the assumption has been that the demon’s information is uncorrelated: its actions at one time do not depend on what it has learned at earlier times. This convenient assumption may neglect some important physics however, especially in a quantum world, where information can be correlated in a “spooky” way. The authors construct a framework for their model in which quantum correlations can be incorporated in full generality and find that correlations can be thermodynamically useful in the same way as energy or uncorrelated information in the original thought experiment. Their framework relies on techniques from condensed matter physics, which are specialized for handling correlations.

Correlated states of knowledge are not the exception, but rather the rule for realistic thermodynamic systems. This research will thus likely cross-fertilize the fields of thermodynamics and condensed matter physics and ignite further such analyses that incorporate correlations.

The full article is available online at


Quantum information is passed along sequentially to the demon, D, determining whether it will exchange energy with a hot thermal bath or a cold thermal bath.


The one-dimensional nature of the model allows for correlated information to be efficiently stored and updated according to the interaction sequence.


Correlations allow for the emergence of a new operational phase, wherein the demon erases and refrigerates simultaneously as it consumes correlations.