Matter and measurement

DAVID A. UCKO

DAVID A. UCKO, BARBARA C. UCKO

Yiqiu Ma, Xiang Li, Sheng-Jun Yang +1 more

The theory of linear quantum measurement has been developed for analysing the sensitivities of experimental devices that measure extremely weak signals, such as gravitational waves. It has successfully contributed to the theoretical understanding of laser interferometer gravitational-wave detectors (used by LIGO, VIRGO and KaGRA) and helped many important experimental upgrades. In this work, we establish a linear quantum measurement theory for another kind of measurement device--- matter wave interferometers, which has been widely discussed as an important platform for many high-precision experiments. This theory allows us to account for both atom and light fluctuations, and leads to a detailed analysis of back-action in matter-wave interferometry (action of light back onto the atoms) and its effect on dynamics and measurement noise. From this analysis, we obtain a Standard Quantum Limit (SQL) for matter-wave interferometry. A comparison between the LIGO detector and matter wave interferometer is also given from the perspective of quantum measurement.

Peiman Ghasemi

Today scientists believe that all “particles” also have a “wave nature” (and vice versa). This phenomenon has been verified not only for elementary particles, but also for the elementary particles that exist in compound particles like molecules and even atoms. You can consider light (the photons of the light beams) as a “wave-like energy”. This energy is a wave–particle, just containing elementary matter and speed. We can use Einstein, Planck equations to determine the amount of the energy which make up a sample photon. But, to date we cannot measure the matter, therefore we make a simple unit that let us to measure the matter.

Ryohei Weil, Dmytro Bondarenko, Arnab Adhikary +1 more

Many symmetry protected or symmetry enriched phases of quantum matter have the property that every ground state in a given such phase endows measurement based quantum computation with the same computational power. Such phases are called computational phases of quantum matter. Here, we experimentally verify four theoretical predictions for them on an IBM superconducting quantum device. We comprehensively investigate how symmetric imperfections of the resource states translate into logical decoherence, and how this decoherence is mitigated. In particular, the central experiment probes the scaling law from which the uniformity of computational power follows. We also analyze the correlated regime, where local measurements give rise to logical operations collectively. We test the prediction that densest packing of a measurement-based algorithms remains the most efficient, in spite of the correlations. Our experiments corroborate the operational stability of measurement based quantum computation in quantum phases of matter with symmetry.

Chris Overstreet, Peter Asenbaum, Mark A. Kasevich

Many different formalisms exist for computing the phase of a matter-wave interferometer. However, it can be challenging to develop physical intuition about what a particular interferometer is actually measuring or about whether a given classical measurement provides equivalent information. Here, we investigate the physical content of the interferometer phase through a series of thought experiments. In low-order potentials, a matter-wave interferometer with a single internal state provides the same information as a sum of position measurements of a classical test object. In high-order potentials, the interferometer phase becomes decoupled from the motion of the interferometer arms, and the phase contains information that cannot be obtained by any set of position measurements on the interferometer trajectory. This phase shift in a high-order potential fundamentally distinguishes matter-wave interferometers from classical measuring devices.