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<\/a><\/p>\nIn\u00a0the\u00a0paper,\u00a0published in\u00a0<\/a>Physical Review Applied<\/a>,\u00a0the\u00a0researchers\u00a0describe how their new sensor, based on Rydberg atoms, can\u00a0determine\u00a0not just the\u00a0electromagnetic field\u00a0strength but also the 3D\u00a0polarization\u00a0orientation and propagation direction,\u00a0known as the k-vector.\u00a0This is the first time such a measurement has been achieved using a quantum sensor.<\/p>\n Traditional sensors can only measure the strength of an\u00a0electromagnetic\u00a0field in one direction at a time. The new ARL-developed sensor, however, can\u00a0\u201csee\u201d\u00a0the\u00a0direction and motion of the\u00a0electromagnetic\u00a0field, providing a complete 3D picture.<\/p>\n Unlike conventional antennas, which\u00a0typically\u00a0must be as large as the signals they detect\u00a0and are often limited to narrow frequency ranges,\u202fARL\u2019s quantum sensor is\u00a0independent of signal\u00a0size,\u00a0just\u00a0a few centimeters across\u00a0and can\u00a0operate\u00a0across the entire radio\u00a0frequency spectrum.\u00a0This property\u00a0stems from the\u00a0broadband capability of Rydberg atoms, which can\u00a0operate\u00a0from direct current to terahertz frequencies, and\u00a0has been\u00a0explored extensively by ARL scientists<\/a>.<\/p>\n Despite\u00a0its\u00a0small size,\u00a0the sensor\u00a0can\u00a0pinpoint the direction of incoming signals with remarkable accuracy, down to about two degrees,\u00a0creating an extremely flexible platform for signal detection.<\/p>\n \u201cThe modern battlefield is an extremely complicated\u00a0radio frequency\u00a0environment,\u201d Meyer said. \u201cWith the proliferation of autonomous systems, there can be hundreds of distinct signal sources.\u00a0Having a single sensor platform that covers the entire radio-frequency\u00a0spectrum and\u00a0can measure\u00a0the 3D direction of those fields\u00a0represents\u00a0a potentially transformative capability, especially\u00a0in spectrum awareness.\u00a0It is\u00a0a great example\u00a0of\u00a0leveraging\u00a0a quantum system\u2019s\u00a0unique\u00a0properties\u00a0to open new possibilities that\u00a0aren\u2019t\u00a0possible with existing technology.\u201d<\/p>\n The sensor uses a tiny glass cell filled with a vapor of rubidium atoms. By shining lasers through the cell, researchers put the atoms into special Rydberg states,\u00a0a highly excited\u00a0state that makes them extremely sensitive to electric fields.\u00a0When a radio wave passes through, the atoms react in a way that reveals not just the strength, but the full 3D direction and movement of the field.<\/p>\n This means the sensor can not only detect the presence of a radio\u00a0signal but\u00a0also\u00a0determine\u00a0exactly where\u00a0the signal is\u00a0coming from and how\u00a0it\u2019s\u00a0moving,\u00a0in three dimensions.<\/p>\n