Proton Still Too Small Despite a proton's tiny size, it is possible to measure its radius bas... more Proton Still Too Small Despite a proton's tiny size, it is possible to measure its radius based on its charge or magnetization distributions. Traditional measurements of proton radius were based on the scattering between protons and electrons. Recently, a precision measurement of a line in the spectrum of muonium—an atom consisting of a proton and a muon, instead of an electron—revealed a radius inconsistent with that deduced from scattering studies. Antognini et al. (p. 417 ; see the Perspective by Margolis ) examined a different spectral line of muonium, with results less dependent on theoretical analyses, yet still inconsistent with the scattering result; in fact, the discrepancy increased.
A measurement of the 2S Lamb shift (2S-2P energy difference) in muonic hydrogen (mu-p) is being p... more A measurement of the 2S Lamb shift (2S-2P energy difference) in muonic hydrogen (mu-p) is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the Lamb shift with 30 ppm precision and to deduce the root mean square (rms) proton charge radius with 10-3 relative accuracy, 20 times more precise than presently known.
The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidi... more The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidium, which is 100 times weaker than the 5S-5D transition, is observed with an extended-cavity diode laser and a vapor cell. Signals with a signal-to-noise ratio of 280 are obtained with a laser power of 10 mW, and the observed linewidth is 3 MHz. The laser wavelength is 760 nm and is locked on the transitions to a stability of 2 x 10(-11). For the first time to our knowledge, the isotope shift of this transition is measured to be 130(4) MHz in atomic frequency.
We report a new determination of muonium 1S-2S transition frequency and its isotope shift with de... more We report a new determination of muonium 1S-2S transition frequency and its isotope shift with deuterium by recalibrating the iodine reference lines using an optical frequency comb. The reference lines for the muonium and deuterium 1S-2S transitions are determined with a precision of 2.4*10^-10 and 1.7*10^-10 respectively. A new muonium-deuterium 1S-2S isotope-shift frequency is derived from these references to be 11 203 464.9(9.2)(4.0) MHz, in agreement with an updated bound-state quantum-electrodynamics prediction based on 2010 adjustments of Committee on Data for Science and Technology and 2.3 times better in the systematic uncertainty than the previous best determination
Quantum tunnelling is a phenomenon of non-equilibrium quantum dynamics and its detailed process i... more Quantum tunnelling is a phenomenon of non-equilibrium quantum dynamics and its detailed process is largely unexplored. We report the experimental observation of macroscopic quantum tunnelling of Bose–Einstein condensate in a hybrid trap. By exerting a non-adiabatic kick to excite a collective rotation mode of the trapped condensate, a periodic pulse train, which remains as condensate, is then out-coupled by quantum tunnelling. This non-equilibrium dynamics is analogue to tunnelling ionization. The imaged tunnelling process shows the splitting of matter wave packet by the potential barrier. The controversial “tunnelling time" question is found inadequate, from the point of view of wave propagation. The realized matter wave pulse train can also be a passive pulsed atom laser for atom interferometer applications.
ABSTRACT Recent experiments are aiming at an accuracy of 1 ppm for the mass of the charged pion u... more ABSTRACT Recent experiments are aiming at an accuracy of 1 ppm for the mass of the charged pion using the characteristic X-rays from exotic atoms. Once the pion mass is established with that precision, the narrow lines from medium Z pionic atoms can be used as a calibration standard in the few keV range. The precision of this new standard is not limited by the large natural line width of fluorescence X-rays and their complex structure due to multi-hole excitations.
ABSTRACT Kinetic energy distributions of muonic hydrogen atoms μp(1S) have been obtained by means... more ABSTRACT Kinetic energy distributions of muonic hydrogen atoms μp(1S) have been obtained by means of a time-of-flight technique for hydrogen gas pressures between 4 and 64 hPa. A high energy component of ∼900 eV observed in the data is interpreted as the signature of long-lived μp(2S) atoms, which are quenched in a non-radiative process leading to the observed high energy: the collision of a thermalized μp(2S) atom with a hydrogen molecule H2 results in the resonant formation of a {[(ppμ)+]*pee}* molecule. Then the (ppμ)+ complex undergoes Coulomb de-excitation and the ∼1.9 keV excitation energy is shared between a μp(1S) atom and one proton. The preliminary analysis of the time spectra gives a long-lived μp(2S) population of ∼1% of all stopped muons, and a quenching rate of ∼4⋅1011 s−1.
Proton Still Too Small Despite a proton's tiny size, it is possible to measure its radius bas... more Proton Still Too Small Despite a proton's tiny size, it is possible to measure its radius based on its charge or magnetization distributions. Traditional measurements of proton radius were based on the scattering between protons and electrons. Recently, a precision measurement of a line in the spectrum of muonium—an atom consisting of a proton and a muon, instead of an electron—revealed a radius inconsistent with that deduced from scattering studies. Antognini et al. (p. 417 ; see the Perspective by Margolis ) examined a different spectral line of muonium, with results less dependent on theoretical analyses, yet still inconsistent with the scattering result; in fact, the discrepancy increased.
A measurement of the 2S Lamb shift (2S-2P energy difference) in muonic hydrogen (mu-p) is being p... more A measurement of the 2S Lamb shift (2S-2P energy difference) in muonic hydrogen (mu-p) is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the Lamb shift with 30 ppm precision and to deduce the root mean square (rms) proton charge radius with 10-3 relative accuracy, 20 times more precise than presently known.
The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidi... more The 5S1/2 --> 7S1/2 two-photon transition of atomic rubidium, which is 100 times weaker than the 5S-5D transition, is observed with an extended-cavity diode laser and a vapor cell. Signals with a signal-to-noise ratio of 280 are obtained with a laser power of 10 mW, and the observed linewidth is 3 MHz. The laser wavelength is 760 nm and is locked on the transitions to a stability of 2 x 10(-11). For the first time to our knowledge, the isotope shift of this transition is measured to be 130(4) MHz in atomic frequency.
We report a new determination of muonium 1S-2S transition frequency and its isotope shift with de... more We report a new determination of muonium 1S-2S transition frequency and its isotope shift with deuterium by recalibrating the iodine reference lines using an optical frequency comb. The reference lines for the muonium and deuterium 1S-2S transitions are determined with a precision of 2.4*10^-10 and 1.7*10^-10 respectively. A new muonium-deuterium 1S-2S isotope-shift frequency is derived from these references to be 11 203 464.9(9.2)(4.0) MHz, in agreement with an updated bound-state quantum-electrodynamics prediction based on 2010 adjustments of Committee on Data for Science and Technology and 2.3 times better in the systematic uncertainty than the previous best determination
Quantum tunnelling is a phenomenon of non-equilibrium quantum dynamics and its detailed process i... more Quantum tunnelling is a phenomenon of non-equilibrium quantum dynamics and its detailed process is largely unexplored. We report the experimental observation of macroscopic quantum tunnelling of Bose–Einstein condensate in a hybrid trap. By exerting a non-adiabatic kick to excite a collective rotation mode of the trapped condensate, a periodic pulse train, which remains as condensate, is then out-coupled by quantum tunnelling. This non-equilibrium dynamics is analogue to tunnelling ionization. The imaged tunnelling process shows the splitting of matter wave packet by the potential barrier. The controversial “tunnelling time" question is found inadequate, from the point of view of wave propagation. The realized matter wave pulse train can also be a passive pulsed atom laser for atom interferometer applications.
ABSTRACT Recent experiments are aiming at an accuracy of 1 ppm for the mass of the charged pion u... more ABSTRACT Recent experiments are aiming at an accuracy of 1 ppm for the mass of the charged pion using the characteristic X-rays from exotic atoms. Once the pion mass is established with that precision, the narrow lines from medium Z pionic atoms can be used as a calibration standard in the few keV range. The precision of this new standard is not limited by the large natural line width of fluorescence X-rays and their complex structure due to multi-hole excitations.
ABSTRACT Kinetic energy distributions of muonic hydrogen atoms μp(1S) have been obtained by means... more ABSTRACT Kinetic energy distributions of muonic hydrogen atoms μp(1S) have been obtained by means of a time-of-flight technique for hydrogen gas pressures between 4 and 64 hPa. A high energy component of ∼900 eV observed in the data is interpreted as the signature of long-lived μp(2S) atoms, which are quenched in a non-radiative process leading to the observed high energy: the collision of a thermalized μp(2S) atom with a hydrogen molecule H2 results in the resonant formation of a {[(ppμ)+]*pee}* molecule. Then the (ppμ)+ complex undergoes Coulomb de-excitation and the ∼1.9 keV excitation energy is shared between a μp(1S) atom and one proton. The preliminary analysis of the time spectra gives a long-lived μp(2S) population of ∼1% of all stopped muons, and a quenching rate of ∼4⋅1011 s−1.
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Papers by Yi-wei Liu