OPTOlogic researchers from ICFO, in collaboration with the University of Warsaw and the Institute of Physics, Polish Academy of Sciences, show how to generate many-body Bell correlated states using ultracold quantum gases in optical lattices.
Quantum Correlations and Their Significance
Quantum correlations are a fundamental aspect of quantum mechanics. They refer to the correlations between the outcomes of measurements performed on two or more particles in a quantum system. These correlations can exhibit strange and counterintuitive behaviors not present in classical systems.
Entanglement and Bell Correlations
The phenomenon of entanglement exemplifies quantum correlations. It describes the correlation between two or more particles, a property that classical physics cannot explain. For example, if two particles entangle, the outcome of the measurement performed on one particle can predict the state of the other, even if the particles are separated by large distances. Bell correlations offer another example, referring to correlations between the outcomes of measurements performed on two or more particles that any local hidden variable theory cannot explain. These correlations often demonstrate the non-classical nature of quantum mechanics and the limitations of classical theories.
Quantum Correlations in Quantum Technologies
Quantum correlations play a key role in developing quantum technologies that exploit the unique properties of quantum systems to perform tasks not possible using classical technologies, including quantum teleportation, quantum cryptography, and quantum computing. However, the generation of many-body Bell correlated states, especially those implemented during the One-Axis Twisting protocol (OAT) procedure, posed an open question for science until now.
Breakthrough in Generating Many-Body Bell Correlated States
In an international study published in Physical Review Letters, ICFO researchers Dr. Marcin Płodzień (also NAWA Bekker 2020 Fellow) and ICREA Prof. Maciej Lewenstein, in collaboration with Prof.Jan Chwedeńczuk from the University of Warsaw and Prof. Emilia Witkowska from the Institute of Physics, Polish Academy of Sciences, have shown that massively correlated quantum many-body states could be generated through current ultracold bosons in optical lattices experiments, using the One-Axis Twisting protocol (OAT) known for generating spin squeezed states.
Spin squeezing states
While entanglement shows how correlated particles can be, spin squeezing is a phenomenon that occurs in a system of particles with a shared quantum state, such as a group of atoms or ions. It involves decreasing as much as possible the uncertainty in the measurement of one of the observables, or “spin” variables, at the expense of increasing the uncertainty in the measurement of the other variables involved.
One-Axis Twisting Protocol (OAT) for Spin Squeezed States
One of the most well-known methods for generating squeezed entangled states is the one-axis twisting protocol (OAT). It can be implemented using various ultra-cold systems interacting through collisions or atom-light interactions and it was well understood that it creates many-body entangled states and two-body Bell correlations.
Novel Insights from the Research
Researchers showed that the one-axis twisting also serves as a viable resource for powerful many-body Bell correlations. They presented a systematic analytical study of creating many-body Bell-correlated states during one-axis twisting dynamics in two-component bosonic systems. They provided the critical time at which the many-body Bell correlations emerge together with a simple yet powerful formula for characterizing the depth of the Bell correlations and entanglement, then applied these findings to classify the generation of many-body Bell correlations in systems of two-component bosons loaded into a one-dimensional optical lattice.
Practical Implications of the Study
The results of this study show that current technology can create such correlations. This holds great importance for potential applications, as Bell correlations can boost the precision of quantum sensors or improve the security of quantum cryptography protocols. Creating such ultra-non-classical many-body states holds fundamental relevance, especially in light of the recent Nobel prize awarded for pioneering studies of such phenomena.
Cited article: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.129.250402
