PRL: Dipolar Bosonic Crystal Orders via Full Distribution Functions

Quantum Simulation of Crystal Formation with Ultracol Dipolar Bosons

The quantum properties underlying crystal formation can be replicated and investigated with the help of ultracold atoms. Our recent paper in Physical Review Letters shows how the use of dipolar atoms enables even the realization and precise measurement of structures that have not yet been observed in any material.

Crystals are ubiquitous in nature. They are formed by many different materials – from mineral salts to heavy metals like bismuth. Their structures emerge because a particular regular ordering of atoms or molecules is favorable, because it requires the smallest amount of energy. A cube with one constituent on each of its eight corners, for instance, is a crystal structure that is very common in nature. A crystal’s structure determines many of its physical properties, such as how well it conducts a current or heat or how it cracks and behaves when it is illuminated by light. But what determines these crystal structures? They emerge as a consequence of the quantum properties of and the interactions between their constituents, which, however, are often scientifically hard to understand and also hard measure.

To nevertheless get to the bottom of the quantum properties of the formation of crystal structures, scientists can simulate the process using Bose-Einstein condensates – trapped ultracold atoms cooled down to temperatures close to absolute zero or minus 273.15 degrees Celsius. The atoms in these highly artificial and highly fragile systems are extremely well under control. With careful tuning, the ultracold atoms behave exactly as if they were the constituents forming a crystal. Although building and running such a quantum simulator is a more demanding task than just growing a crystal from a certain material, the method offers two main advantages: First, scientists can tune the properties for the quantum simulator almost at will, which is not possible for conventional crystals. Second, the standard readout of cold-atom quantum simulators are images containing information about all crystal particles. For a conventional crystal, by contrast, only the exterior is visible, while the interior – and in particular its quantum properties – is difficult to observe.

Our paper demonstrates that a quantum simulator for crystal formation is much more flexible when it is built using ultracold dipolar quantum particles. Dipolar quantum particles make it possible to realize and investigate not just conventional crystal structures, but also arrangements that were hitherto not seen for any material. The study explains how these crystal orders emerge from an intriguing competition between kinetic, potential, and interaction energy and how the structures and properties of the resulting crystals can be gauged in unprecedented detail.

Read more at PRL and at .

See this page for the press release and this video with an interview about the paper by its lead author Budhaditya Chatterjee.


Quantum Science and Technology: MCTDH-X software tutorial paper published

We introduce and describe the multiconfigurational time-depenent Hartree for indistinguishable particles (MCTDH-X) software, which is hosted, documented, and distributed at

We give an introduction to the MCTDH-X software via an easy-to-follow tutorial with a focus on accessibility. The illustrated exemplary
problems are hosted at and consider the physics of a few interacting bosons or
fermions in a double-well potential.

A complete set of input files and scripts to redo all computations in this paper is provided at, accompanied by tutorial videos at

Read more at Quantum Science and Technology and arXiv.

RMP Colloquium on MCTDH-X et al.

In this Colloquium, the wavefunction-based Multiconfigurational Time-Dependent Hartree approaches to the dynamics of indistinguishable particles (MCTDH-F for Fermions and MCTDH-B for Bosons) are reviewed. MCTDH-B and MCTDH-F or, together, MCTDH-X are methods for describing correlated quantum systems of identical particles by solving the time-dependent Schrödinger equation from first principles. 

We highlight some applications to instructive and experimentally-realized quantum many-body systems: the dynamics of atoms in Bose-Einstein condensates in magneto-optical and optical traps and of electrons in atoms and molecules.

We discuss the current development and frontiers in the field of MCTDH-X: theories and numerical methods for indistinguishable particles, for mixtures of multiple species of indistinguishable particles, the inclusion of nuclear motion for the nonadiabatic dynamics of atomic and molecular systems, as well as the multilayer and second-quantized-representation approaches, and the orbital-adaptive time-dependent coupled-cluster theory are discussed.

Read more at Review of Modern Physics and arXiv:1908.03578 [cond-mat.quant-gas]

PRA: Superfluid -- Mott insulator transition of ultracold superradiant bosons in a cavity

Superfluid--Mott insulator transition of ultracold superradiant bosons in a cavity

We analyze the rich physics of the superfluid-to-Mott-insulator transition of ultracold interacting bosons in an optical cavity.

We explore the whole phase diagram of the system and underpin our MCTDH-X results with analytical considerations.

Read more at arxiv and Phys. Rev. A. .

NJP: Correlations of ultracold dipolar bosons in optical lattices

Correlations of strongly interacting ultracold dipolar bosons in optical lattices

We explore and analyze the rich structure of correlations of ultracold bosons with dipolar interactions in optical lattices and demonstrate that their quantum phases may be inferred from them.

Read more at arxiv and NJP.

NJP: Managing the Correlations of Ultracold Bosons in Triple Wells

Management of the correlations of Ultracold Bosons in triple wells

We investigated the correlations of ultracold many-boson systems in tilted triple wells with contact and dipolar interactions.

We were able to put forward a protocol to manage the correlation functions of the many-body state by tuning the depth and tilt of the lattice and the strength of the interactions between the particles.

Read more at arxiv and at NJP.




PRX: Granulation and Faraday waves in driven quantum systems

Parametric excitation of a Bose-Einstein condensate: From Faraday waves to granulation

Surprisingly, the quantum version of granulation and Faraday waves can be produced in the same quantum system: a gas of trapped atoms cooled very close to absolute zero temperature.

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NJP: Fragmented superradiance and polarization in two-component Bose-Einstein condensates in a cavity

Many-body physics in two-component Bose–Einstein condensates in a cavity: fragmented superradiance and polarization

Rich many-body physics arise in interacting laser-pumped ultracold two-component bosons in a cavity.

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PRA: Superlattice switching in a driven-dissipative Bose-Einstein condensate in a cavity

PRA: Superlattice switching in a driven-dissipative Bose-Einstein condensate in a cavity

We have explored a resonance between a Bose-Einstein condensate in a cavity and photons by modulating the pump laser power.

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PRA: Entropies and correlations of ultracold bosons in a lattice

Entropies and correlations of ultracold bosons in a lattice

The collective behavior of interacting bosons in lattices comes in many different flavors.

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