arXiv subjects

J. R. Torgerson

Publications and source records attributed to J. R. Torgerson.

17 recordsLinked to original sources

arXiv2013

New limits on variation of the fine-structure constant using atomic dysprosium

We report on the spectroscopy of radio-frequency transitions between nearly-degenerate, opposite-parity excited states in atomic dysprosium (Dy). Theoretical calculations predict that these states are very sensitive to variation of the fine-structure constant, $α$, owing to large relativistic corrections of opposite sign for the opposite-parity levels. The near degeneracy reduces the relative precision necessary to place constraints on variation of $α$ competitive with results obtained from the best atomic clocks in the world. Additionally, the existence of several abundant isotopes of Dy allows isotopic comparisons that suppress common-mode systematic errors. The frequencies of the 754-MHz transition in $^{164}$Dy and 235-MHz transition in $^{162}$Dy were measured over the span of two years. Linear variation of $α$ is found to be $\dotα/α= (-5.8\pm6.9)\times10^{-17}$ yr$^{-1}$, consistent with zero. The same data are used to constrain the dimensionless parameter $k_α$, characterizing a possible coupling of $α$ to a changing gravitational potential. We find that $k_α= (-5.5\pm5.2)\times10^{-7}$, essentially consistent with zero and the best constraint to date.

physics.atom-ph↗

arXiv2010

Progress towards fabrication of Th:229-doped high energy band-gap crystals for use as a solid-state optical frequency reference

We have recently described a novel method for the construction of a solid-state optical frequency reference based on doping $^{229}$Th into high energy band-gap crystals. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we have argued that the $^{229}$Th optical nuclear transition may be driven inside a host crystal resulting in an optical frequency reference with a short-term stability of $3\times10^{-17}<Δf/f <1\times10^{-15}$ at 1 s and a systematic-limited repeatability of $Δf/f \sim 2 \times 10^{-16}$. Improvement by $10^2-10^3$ of the constraints on the variability of several important fundamental constants also appears possible. Here we present the results of the first phase of these experiments. Specifically, we have evaluated several high energy band-gap crystals (Th:NaYF, Th:YLF, Th:LiCAF, Na$_2$ThF$_6$, LiSAF) for their suitability as a crystal host by a combination of electron beam microprobe measurements, Rutherford Backscattering, and synchrotron excitation/fluorescence measurements. These measurements have shown LiCAF to be the most promising host crystal, and using a $^{232}$Th doped LiCAF crystal, we have performed a mock run of the actual experiment that will be used to search for the isomeric transition in $^{229}$Th. This data indicates that a measurement of the transition energy with a signal to noise ratio (SNR) greater than 30:1 can be achieved at the lowest expected fluorescence rate.

physics.atom-ph↗

arXiv2010

Quantum dense coding without entanglement

We describe a quantum cryptography protocol with up to twenty four-dimensional ($\mathcal{D} =4$) states generated by a polarization-, phase- and time-encoding transmitter. This protocol can be experimentally realized with existing technology, drawing from time-encoded and polarization-encoded systems. The protocol is error tolerant and has a quantum bit-rate of 2 per transmission/detection, which when combined with state detection efficiency yields a qubit efficiency of up to 1 or double that of BB84-{\it like} protocols.

quant-ph↗

arXiv2010

Transverse laser cooling of a thermal atomic beam of dysprosium

A thermal atomic beam of dysprosium (Dy) atoms is cooled using the $4f^{10}6s^2 (J=8) \to 4f^{10}6s6p (J=9)$ transition at 421 nm. The cooling is done via a standing light wave orthogonal to the atomic beam. Efficient transverse cooling to the Doppler limit is demonstrated for all observable isotopes of dysprosium. Branching ratios to metastable states are demonstrated to be $<5\times10^{-4}$. A scheme for enhancement of the nonzero-nuclear-spin-isotope cooling, as well as a method for direct identification of possible trap states, is proposed.

physics.atom-ph↗

arXiv2010

Optical transition of the $^{229}$Th nucleus in a solid-state environment

We describe a novel approach to directly measure the energy of the narrow, low-lying isomeric state in $^{229}$Th. Since nuclear transitions are far less sensitive to environmental conditions than atomic transitions, we argue that the $^{229}$Th optical nuclear transition may be driven inside a host crystal with a high transition Q. This technique might also allow for the construction of a solid-state optical frequency reference that surpasses the precision of current optical clocks, as well as improved limits on the variability of fundamental constants. Based on analysis of the crystal lattice environment, we argue that a precision of $3\times10^{-17}<Δf/f <1\times10^{-15}$ after 1 s of photon collection may be achieved with a systematic-limited accuracy of $Δf/f \sim 2 \times 10^{-16}$. Improvement by $10^2-10^3$ of the constraints on the variability of several important fundamental constants also appears possible.

physics.atom-ph↗

arXiv2009

Transition frequency shifts with fine-structure constant variation for Yb II

In this paper we report calculations of the relativistic corrections to transition frequencies (q factors) of Yb II for the transitions from the odd-parity states to the metastable state $4f^{13}6s^2 ^2F_{7/2}^o$. These transitions are of particular interest experimentally since they possess some of the largest q factors calculated to date and the $^2F_{7/2}^o$ state can be prepared with high efficiency. This makes Yb II a very attractive candidate for the laboratory search for variation of the fine-structure constant alpha.

physics.atom-ph↗

arXiv2008

Variation of the Fine-Structure Constant and Laser Cooling of Atomic Dysprosium

Radio-frequency electric-dipole transitions between nearly degenerate, opposite parity levels of atomic dysprosium (Dy) were monitored over an eight-month period to search for a variation in the fine-structure constant, $α$. The data provide a rate of fractional temporal variation of $α$ of $(-2.4\pm2.3)\times10^{-15}$ yr$^{-1}$ or a value of $(-7.8 \pm 5.9) \times 10^{-6}$ for $k_α$, the variation coefficient for $α$ in a changing gravitational potential. All results indicate the absence of significant variation at the present level of sensitivity. We also present initial results on laser cooling of an atomic beam of dysprosium.

physics.atom-ph↗

arXiv2007

Investigation of the Gravitational Potential Dependence of the Fine-Structure Constant Using Atomic Dysprosium

Radio-frequency E1 transitions between nearly degenerate, opposite parity levels of atomic dysprosium were monitored over an eight month period to search for a variation in the fine-structure constant. During this time period, data were taken at different points in the gravitational potential of the Sun. The data are fitted to the variation in the gravitational potential yielding a value of $(-8.7 \pm 6.6) \times 10^{-6}$ for the fit parameter $k_α$. This value gives the current best laboratory limit. In addition, our value of $k_α$ combined with other experimental constraints is used to extract the first limits on k_e and k_q. These coefficients characterize the variation of m_e/m_p and m_q/m_p in a changing gravitational potential, where m_e, m_p, and m_q are electron, proton, and quark masses. The results are $k_e = (4.9 \pm 3.9) \times 10^{-5}$ and $k_q = (6.6 \pm 5.2) \times 10^{-5}$.

physics.atom-ph↗

arXiv2007

Dressed Spin of Helium-3

We report a measurement of dressed-spin effects of polarized 3He atoms from a cold atomic source traversing a region of constant magnetic field B0 and a transverse oscillatory dressing field Bd cos(omega * t). The observed effects are compared with a numerical simulation using the Bloch equation as well as a calculation based on the dressed-atom formalism. An application of the dressed spin of 3He for a proposed neutron electric dipole moment measurement is also discussed.

nucl-ex↗

arXiv2006

Limit on the Temporal Variation of the Fine-Structure Constant Using Atomic Dysprosium

Over a period of eight months, we have monitored transition frequencies between nearly degenerate, opposite-parity levels in two isotopes of atomic dysprosium (Dy). These transition frequencies are highly sensitive to temporal variation of the fine-structure constant ($α$) due to relativistic corrections of large and opposite sign for the opposite-parity levels. In this unique system, in contrast to atomic-clock comparisons, the difference of the electronic energies of the opposite-parity levels can be monitored directly utilizing a radio-frequency (rf) electric-dipole transition between them. Our measurements show that the frequency variation of the 3.1-MHz transition in $^{163}$Dy and the 235-MHz transition in $^{162}$Dy are 9.0$\pm$6.7 Hz/yr and -0.6$\pm$6.5 Hz/yr, respectively. These results provide a value for the rate of fractional variation of $α$ of $(-2.7\pm2.6)\times 10^{-15}$ yr$^{-1}$ (1 $σ$) without any assumptions on the constancy of other fundamental constants, indicating absence of significant variation at the present level of sensitivity.

physics.atom-ph↗

arXiv2005

Collisional perturbation of radio-frequency E1 transitions in an atomic beam of dysprosium

We have studied collisional perturbations of radio-frequency (rf) electric-dipole (E1) transitions between the nearly degenerate opposite-parity levels in atomic dysprosium (Dy) in the presence of 10 to 80 $μ$Torr of H$_\text{2}$, N$_\text{2}$, He, Ar, Ne, Kr, and Xe. Collisional broadening and shift of the resonance, as well as the attenuation of the signal amplitude are observed to be proportional to the foreign-gas density with the exception of H$_2$ and Ne, for which no shifts were observed. Corresponding rates and cross sections are presented. In addition, rates and cross sections for O$_2$ are extracted from measurements using air as foreign gas. The primary motivation for this study is the need for accurate determination of the shift rates, which are needed in a laboratory search for the temporal variation of the fine-structure constant [A. T. Nguyen, D. Budker, S. K. Lamoreaux, and J. R. Torgerson, Phys. Rev. A \textbf{69}, 22105 (2004)].

physics.atom-ph↗

arXiv2004

Optical Velocimetry

This work considers current potential uses of laser Doppler velocimetry. A discussion of other optical velocimetry techniques is presented and compared with their practical application to modern shock physics diagnostics, such as VISAR.

physics.optics↗

arXiv2004

The Low-Frequency Character of the Thermal Correction to the Casimir Force between Metallic Films

The frequency spectrum of the finite temperature correction to the Casimir force can be determined by use of the Lifshitz formalism for metallic plates of finite conductivity. We show that the correction for the $TE$ electromagnetic modes is dominated by frequencies so low that the plates cannot be modelled as ideal dielectrics. We also address issues relating to the behavior of electromagnetic fields at the surfaces and within metallic conductors, and calculate the surface modes using appropriate low-frequency metallic boundary conditions. Our result brings the thermal correction into agreement with experimental results that were previously obtained. We suggest a series of measurements that will test the veracity of our analysis.

quant-ph↗

arXiv2004

The Low-Frequency Character of the Thermal Correction to the Casimir Force between Metallic Films

The frequency spectrum of the finite temperature correction to the Casimir force can be determined by the use of the Lifshitz formalism for metallic plates of finite conductivity. We show that the correction for the TE electromagnetic modes is dominated by frequencies so low that the plates cannot be modelled as ideal dielectrics. We also address the issues relating to the behavior of electromagnetic fields at the surfaces an within metallic conductors, and claculate the surface modes using appropriate low-frequency metallic boundary conditions. Our result brings the tehrmal correction into agreement with experimental results that were previously obtained.

quant-ph↗

arXiv2003

Towards a sensitive search for variation of the fine structure constant using radio-frequency E1 transitions in atomic dysprosium

It has been proposed that the radio-frequency electric-dipole (E1) transition between two nearly degenerate opposite-parity states in atomic dysprosium should be highly sensitive to possible temporal variation of the fine structure constant ($α$) [V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A {\bf 59}, 230 (1999)]. We analyze here an experimental realization of the proposed search in progress in our laboratory, which involves monitoring the E1 transition frequency over a period of time using direct frequency counting techniques. We estimate that a statistical sensitivity of $|\adota| \sim 10^{-18}$/yr may be achieved and discuss possible systematic effects that may limit such a measurement.

physics.atom-ph↗

arXiv2003

Fast, efficient error reconciliation for quantum cryptography

We describe a new error reconciliation protocol {\it Winnow} based on the exchange of parity and Hamming's ``syndrome'' for $N-$bit subunits of a large data set. {\it Winnow} was developed in the context of quantum key distribution and offers significant advantages and net higher efficiency compared to other widely used protocols within the quantum cryptography community. A detailed mathematical analysis of Winnow is presented in the context of practical implementations of quantum key distribution; in particular, the information overhead required for secure implementation is one of the most important criteria in the evaluation of a particular error reconciliation protocol. The increase in efficiency for Winnow is due largely to the reduction in authenticated public communication required for its implementation.

quant-ph↗

arXiv2001

Method for Precision Test of Fine Structure Constant Variation with Optical Frequency References

A new method for examining the possible space-time variation of the fine structure constant ($α$) is proposed. The technique uses a relatively simple measurement with an optical resonator to compare atom-stabilized optical frequency references. This method does not require that the exact frequency of each reference be measured, and has the potential to yield more than a 1000-fold improvement in experimental sensitivity to changes in $α$. A specific realization of an experiment using this method is discussed which can approach the precision of ${\dotα/α}\sim10^{-18}/τ$, where $τ$ is the measurement time. Moreover, for this specific realization, a measurement of ${\dotα/α}\sim10^{-15}/{\rm yr}$ as a near-term goal is realistic.

physics.atom-ph↗