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Fig. 1a: chematic of TDBG with a twist angle θ.

Tunable Spin-Polarized Correlated States in Twisted Double Bilayer Graphene

July 9, 2020

Reducing the energy bandwidth of electrons in a lattice below the long-range Coulomb interaction energy promotes correlation effects. Moiré superlattices—which are created by stacking van der Waals heterostructures with a controlled twist angle—enable the engineering of electron band structure. Exotic quantum phases can emerge in an engineered moiré flat band. The recent discovery of correlated insulator states, superconductivity and the quantum anomalous Hall effect in the flat band of magic-angle twisted bilayer graphene has sparked the exploration of correlated electron states in...

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Forming a Single Molecule in an Optical Tweezer (artist's representation)

Longer Lived Molecules

July 1, 2020

Individual molecules placed in precisely defined quantum states could provide the building blocks for molecular arrays for quantum computing applications. But first, researchers need to develop techniques for creating these molecules. Now Jessie Zhang at Harvard University and colleagues demonstrate such a technique for forming a long-lived single NaCs molecule in a specific, reversible quantum state...

Continue reading "Longer Lived Molecules" by...

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Shut Down STEM poster

Towards a More Inclusive Physics Community

June 14, 2020

On June 10, 2020, the Department held a special department-wide meeting of the Equity & Inclusion Committee for a discussion focusing on how we can increase the number of African American physicists. Introductory comments by Department Chair, Prof. Subir Sachdev, are below.

Dear all,

I would like to make some personal remarks to mark the deaths of George Floyd, Ahmaud Arbery, Breonna Taylor, and many others, and recent national events.

I grew up in India and have spent my adult life in America. India and America have much in...

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Vafa book cover

"Puzzles to Unravel the Universe" -- New Book by Prof. Cumrun Vafa

June 12, 2020

Beneath all of the complex and formidable mathematical structures that formulate physical laws rest simple but deep nuggets of truth. It is these simple truths, and not the complicated technical details, that scientists strive for when uncovering the laws of nature. Fortunately, these core ideas can often be illustrated with simple mathematical puzzles. These puzzles are so simplified that one can tackle them and appreciate their meaning without using any complicated math. 

A new book by Prof. Cumrun Vafa, Puzzles to Unravel the Universe, aims to take the reader...

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Figure 1: a new refrigerator for molecules

Collisional Cooling of Ultracold Molecules

April 8, 2020

A diatomic molecule consists of two atoms, held together by a chemical bond. But these molecules are more than just a pair of atoms: if one atom is different from the other, the molecules become polar. This polarity empowers the diatomic molecules to strongly interact with each other, even at long distance. These molecules can also vibrate or rotate--something that single atoms cannot do--giving us extra-knobs to control their quantum behavior. These special features of the molecules make them important and powerful candidates for quantum computers and quantum simulators as well as a...

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figure 1 from the article: Phase diagram of the 2D Rydberg Hamiltonian

Phases of a Two-Dimensional Rydberg Atom Array

March 31, 2020

The ability to fully control coherent quantum many-body systems is an exciting and rapidly developing frontier. Besides quantum information processing, controlled many-body systems can enable new insights into strongly correlated phases of matter. On this front, arrays of neutral atoms trapped in optical tweezers and interacting via controlled excitations into atomic Rydberg states provide an especially promising platform. In fact, their particular properties have allowed for the programmable realization and high-fidelity manipulation of a wide range of effective interacting spin models...

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Figure 1: Sample video, questions, and answers from our CoLlision Events for Video Representation and Reasoning (CLEVRER) dataset.

A Hybrid AI Model Lets It Reason about the World’s Physics Like a Child

March 6, 2020

A new data set reveals just how bad AI is at reasoning—and suggests that a new hybrid approach might be the best way forward.

Questions, questions: Known as CLEVRER, the data set consists of 20,000 short synthetic video clips and more than 300,000 question and answer pairings that reason about the events in the videos. Each video shows a simple world of toy objects that collide with one another following simulated physics. In one, a red rubber ball hits a blue rubber cylinder...

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Book cover for "The Second Kind of Impossible"

Harvard Science Book Talk: Paul Steinhardt, "The Second Kind of Impossible"

March 5, 2020

THE SECOND KIND OF IMPOSSIBLE tells one of the strangest scientific stories that you will ever hear – a thirty-five year quest for new forms of matter, known as quasicrystals, that violate scientific principles that had been established for centuries. The talk will describe the scientific odyssey that unfolds over the ensuing decades, first to prove the validity of the idea, and then to pursue Steinhardt's wildest conjecture: that nature made quasicrystals long before humans discovered them. Along the way, his team encounters clandestine collectors, corrupt scientists, secret...

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Schematic drawing of the resistivity of magic-angle graphene

Experiments on magic-angle graphene reveal a “strange metal” phase and transport behavior consistent with so-called Planckian dissipation

February 20, 2020

Magic-angle graphene captured the attention of condensed-matter physicists in 2018 when it was discovered that this material—made of two sheets of graphene with slightly misaligned lattice orientations—is a superconductor. Moreover, observations showed that the phase diagram of magic-angle graphene is similar to that of copper oxide high-temperature superconductors, with an insulating region next to a dome-shaped superconducting region. Now, Pablo Jarillo-Herrero from the Massachusetts Institute of Technology, Cambridge, and his colleagues report that magic-angle graphene...

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