arXiv subjects

Stephen D. Hogan

Publications and source records attributed to Stephen D. Hogan.

3 recordsLinked to original sources

arXiv2025

Nonclassicality of a Macroscopic Qubit-Ensemble via Parity Measurement Induced Disturbance

We propose an experimental scheme to test the nonclassicality of a macroscopic ensemble of qubits, through the violation of the classical notion of macrorealism (MR) via the fundamental measurement-induced disturbance of quantum systems. An electromagnetic resonator is used to probe the parity of the qubit-ensemble. The action of sequential measurements allows the nonclassicality of whole ensemble to manifest itself, in the ideal case, irrespective of its size. This enables to probe the macroscopic limits of quantum mechanics as the qubit-ensemble is, effectively, a single large spin of many $\hbar$ units. Even as $\hbar \rightarrow 0$ in comparison to the total angular momentum of the ensemble, a constant amount of violation of MR is found in the noiseless case. However, environmental decoherence and inhomogeneity of qubit-electromagnetic field couplings precipitate the quantum-to-classical transition. This implies that Bohr's correspondence principle is not fundamental, but a consequence of practical limitations. We outline an implementation with a variety of qubits (superconducting qubits, spins in semiconductors, and Rydberg atoms) coupled to a coplanar waveguide resonator, and - via the corresponding noise analysis - find that violation of MR is detectable up to $100$ qubits via current technology.

quant-ph↗

arXiv2016

Rydberg-Stark deceleration of atoms and molecules

The large electric dipole moments associated with highly excited Rydberg states of atoms and molecules make gas-phase samples in these states very well suited to deceleration and trapping using inhomogeneous electric fields. The methods of Rydberg-Stark deceleration with which this can be achieved are reviewed here. Using these techniques, the longitudinal motion of beams of atoms and molecules moving at speeds as high as 2500~m/s have been manipulated, with changes in kinetic energy of up to $|ΔE_{\mathrm{kin}}|=1.3\times10^{-20}$~J ($|ΔE_{\mathrm{kin}}|/e=80$~meV or $|ΔE_{\mathrm{kin}}|/hc=650$~cm$^{-1}$) achieved, while decelerated and trapped samples with number densities of $10^6$--$10^7$~cm$^{-3}$ and translational temperatures of $\sim150$~mK have been prepared. Applications of these samples in areas of research at the interface between physics and physical chemistry are discussed.

physics.atom-ph↗

arXiv2011

Multistage Zeeman deceleration of metastable neon

A supersonic beam of metastable neon atoms has been decelerated by exploiting the interaction between the magnetic moment of the atoms and time-dependent inhomogeneous magnetic fields in a multistage Zeeman decelerator. Using 91 deceleration solenoids, the atoms were decelerated from an initial velocity of 580m/s to final velocities as low as 105m/s, corresponding to a removal of more than 95% of their initial kinetic energy. The phase-space distribution of the cold, decelerated atoms was characterized by time-of-flight and imaging measurements, from which a temperature of 10mK was obtained in the moving frame of the decelerated sample. In combination with particle-trajectory simulations, these measurements allowed the phase-space acceptance of the decelerator to be quantified. The degree of isotope separation that can be achieved by multistage Zeeman deceleration was also studied by performing experiments with pulse sequences generated for $^{20}$Ne and $^{22}$Ne.

physics.atom-ph↗