Optical implementation of spin squeezing

Abstract

Quantum metrology enables estimation of optical phase shifts with precision beyond the shot-noise limit. One way to exceed this limit is to use squeezed states, where the quantum noise of one observable is reduced at the expense of increased quantum noise for its complementary partner. Because shotnoise limits the phase sensitivity of all classical states, reduced noise in the average value for the observable being measured allows for improved phase sensitivity. However, additional phase sensitivity can be achieved using phase estimation strategies that account for the full distribution of measurement outcomes. Here we experimentally investigate a model of optical spin-squeezing, which uses post-selection and photon subtraction from the state generated using a parametric downconversion photon source, and we investigate the phase sensitivity of this model. The Fisher information for all photon-number outcomes shows it is possible to obtain a quantum advantage of 1.58 compared to the shot-noise value for five-photon events, even though due to experimental imperfection, the average noise for the relevant spin-observable does not achieve sub-shot-noise precision. Our demonstration implies improved performance of spin squeezing for applications to quantum metrology.

Magic state distillation from entangled states

“…We then perform a global entangling unitary usually used in spin squeezing procedures [49] on such states and examine how it improves distillation outcome. Spin squeezed states have been implemented in atomic cavities going back a couple of decades, primarily with application to quantum metrology and detecting quantum entanglement [50][51][52][53][54][55].…”

“…Heuristically, we can also see spin squeezing as reducing what is otherwise an infinite distillation cost to a finite number as none of the intial input states were distillable. This is another clear demonstration that entangled states generated in a more practical laboratory setting [50][51][52][53] can help enhance the outcome of magic state distillation. While this is encouraging, squeezing does not always improve distillation outcomes.…”

Generation of single- and two-mode multiphoton states in waveguide QED

“…As the dual Fock states can be generated efficiently with our protocols (see discussion on Holland-Burnett-States), one only needs to add one single excitation over the two metastable states at the end. Other proposals for the generation of Yurke states using linear optical setups, e.g., by photon substraction [45] are also possible by using the transitions between metastable states.…”

Nonclassical states of light with a smooth P function

“…Creating and characterizing nonclassical states of light are two tasks of substantial interest in a wide range of applications [1,2], such as sub-shot-noise measurements [3][4][5], high resolution imaging [6][7][8][9], light source and detector calibration [10][11][12], quantum cryptography [13,14], or quantum information processing [15].…”