Imaging twisty magnets Twisting monolayers of graphene with respect to each other has led to a number of unusual correlated states. This approach has inspired researchers to try their hand at twisting two-dimensional (2D) magnets, but such experiments have proven a difficult challenge. Song et al . made structures out of layers of the 2D magnet chromium triiodide with a small twist angle (see the Perspective by Lado). Using nitrogen vacancy centers in diamond as a magnetometer, the authors imaged the magnetic domains in both twisted monolayer and twisted trilayer structures. For twisted trilayers, a periodic pattern of ferromagnetic and antiferromagnetic domains was revealed. —JS

Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism ( i.e. , synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.

The emergence of atomically thin van der Waals magnets provides a new platform for the studies of two-dimensional magnetism and its applications. However, the widely used measurement methods in recent studies cannot provide quantitative information of the magnetization nor achieve nanoscale spatial resolution. These capabilities are essential to explore the rich properties of magnetic domains and spin textures. Here, we employ cryogenic scanning magnetometry using a single-electron spin of a nitrogen-vacancy center in a diamond probe to unambiguously prove the existence of magnetic domains and study their dynamics in atomically thin CrBr3. By controlling the magnetic domain evolution as a function of magnetic field, we find that the pinning effect is a dominant coercivity mechanism and determine the magnetization of a CrBr3 bilayer to be about 26 Bohr magnetons per square nanometer. The high spatial resolution of this technique enables imaging of magnetic domains and allows to locate the sites of defects that pin the domain walls and nucleate the reverse domains. Our work highlights scanning nitrogen-vacancy center magnetometry as a quantitative probe to explore nanoscale features in two-dimensional magnets.

Bit commitment is a fundamental cryptographic task that guarantees a secure commitment between two mutually mistrustful parties and is a building block for many cryptographic primitives, including coin tossing 1, 2 , zero-knowledge proofs 3, 4 , oblivious transfer 5, 6 and secure two-party computation 7 . Unconditionally secure bit commitment was thought to be impossible 8-13 until recent theoretical protocols that combine quantum mechanics and relativity were shown to elude previous impossibility proofs 14-17 . Here we implement such a bit commitment protocol 17 . In the experiment, the committer performs quantum measurements using two quantum key distribution systems 18 and the results are transmitted via free-space optical communication to two agents separated with more 1

Quantum teleportation [1] faithfully transfers a quantum state between distant nodes in a network, enabling revolutionary information processing applications [2][3][4]. Here we report teleporting quantum states over a 30 km optical fibre network with the input single photon state and the EPR state prepared independently. By buffering photons in 10 km coiled optical fibre, 1