Quantum sensing refers to the use of a quantum system to perform a measurement of a physical quantity. Such sensors utilize properties of quantum mechanics such as entanglement, quantum interference, and quantum state squeezing. This allows quantum sensors to detect minute changes in electric or magnetic fields, enabling precision measurements.

Analogous to the DiVincenzo criteria for quantum computers, a set of four criteria must be met for a quantum system to function as a quantum sensor:

- The quantum system must have discrete, resolvable energy levels.
- You can initialize the quantum system into a well-known state and you can perform a readout of the quantum system state.
- You can coherently manipulate the quantum system
- The quantum system must interact with a physical quantity and therefore have a response to that quantity.

Quantum sensors have a wide range of applications in the fields of microscopy, communication technology, and medicine. Historical examples of quantum sensors include atomic clocks, superconducting quantum interference devices, and magnetometers. In addition to photonic devices, quantum sensing can also be used in areas such as trapped ions, spin qubits, and flux qubits. The current PQI researchers lead a research effort that promises technological advancements and a deeper understanding of quantum sensors.

PQI researchers work on a wide range of quantum sensing technologies:

- The Dutt group uses nitrogen-vacancy (NV) centers as potential quantum sensors able to detect weak magnetic fields with nanometer spatial resolution.
- The Purdy group is interested in harnessing the quantum effects intrinsic to the mechanical interaction of light with macroscopic mechanical resonators to improve measurement and metrology.

Below is a list of publications in quantum sensing:

- Precision in quantum sensing requires the maximum field strength to be much less than the spectral linewidth of the sensor. The Dutt group in their Nature Communication publication implemented novel phase estimation algorithms on a single electronic spin in a nitrogen-vacancy center in a diamond to achieve a significant improvement in the ratio of the maximum field strength to precision.