arXiv subjects

D. B. Hume

Publications and source records attributed to D. B. Hume.

17 recordsLinked to original sources

arXiv2023

Quantum metrology algorithms for dark matter searches with clocks

Quantum algorithms such as dynamical decoupling can be used to improve the sensitivity of a quantum sensor to a signal while suppressing sensitivity to noise. Atomic clocks are among the most sensitive quantum sensors, with recent improvements in clock technology allowing for unprecedented precision and accuracy. These clocks are highly sensitive to variations in fundamental constants, making them ideal probes for local ultralight scalar dark matter. Further improvements to the sensitivity is expected in proposed nuclear clocks based on the thorium 229m isomer. We investigate the use of various quantum metrology algorithms in the search for dark matter using quantum clocks. We propose a new broadband dynamical decoupling algorithm and compare it with quantum metrology protocols that have been previously proposed and demonstrated, namely differential spectroscopy and narrowband dynamical decoupling. We conduct numerical simulations of scalar dark matter searches with realistic noise sources and accounting for dark matter decoherence. Finally, we discuss an alternative thorium nuclear transition excitation method that bypasses the technical challenges associated with vacuum ultraviolet lasers.

quant-ph↗

arXiv2020

Lifetime-Limited Interrogation of Two Independent ${}^{27}\textrm{Al}^{+}$ Clocks Using Correlation Spectroscopy

Laser decoherence limits the stability of optical clocks by broadening the observable resonance linewidths and adding noise during the dead time between clock probes. Correlation spectroscopy avoids these limitations by measuring correlated atomic transitions between two ensembles, which provides a frequency difference measurement independent of laser noise. Here, we apply this technique to perform stability measurements between two independent clocks based on the $^1S_0\leftrightarrow{}^3P_0$ transition in $^{27}$Al$^+$. By stabilizing the dominant sources of differential phase noise between the two clocks, we observe coherence between them during synchronous Ramsey interrogations as long as 8 s at a frequency of $1.12\times10^{15}$ Hz. The observed contrast in the correlation spectroscopy signal is consistent with the 20.6 s $^3P_0$ state lifetime and supports a measurement instability of $(1.8\pm0.5)\times 10^{-16}/\sqrt{τ/\textrm{s}}$ for averaging periods longer than the probe duration when deadtime is negligible.

physics.atom-ph↗

arXiv2019

Systematic uncertainty due to background-gas collisions in trapped-ion optical clocks

We describe a framework for calculating the frequency shift and uncertainty of trapped-ion optical atomic clocks caused by background-gas collisions, and apply this framework to an $^{27}$Al$^+$ clock to enable a total fractional systematic uncertainty below $10^{-18}$. For this clock, with 38(19) nPa of room temperature H$_2$ background gas, we find that collisional heating generates a non-thermal distribution of motional states with a mean time-dilation shift of order $10^{-16}$ at the end of a 150 ms probe, which is not detected by sideband thermometry energy measurements. However, the contribution of collisional heating to the spectroscopy signal is highly suppressed and we calculate the BGC shift to be $-0.6(2.4)\times 10^{-19}$, where the shift is due to collisional heating time-dilation and the uncertainty is dominated by the worst case $\pm π/2$ bound used for collisional phase shift of the $^{27}$Al$^+$ superposition state. We experimentally validate the framework and determine the background-gas pressure in situ using measurements of the rate of collisions that cause reordering of mixed-species ion pairs.

physics.atom-ph↗

arXiv2019

Measurements of $^{27}$Al$^{+}$ and $^{25}$Mg$^{+}$ magnetic constants for improved ion clock accuracy

We have measured the quadratic Zeeman coefficient for the ${^{1}S_{0} \leftrightarrow {^{3}P_{0}}}$ optical clock transition in $^{27}$Al$^{+}$, $C_{2}=-71.944(24)$~MHz/T$^{2}$, and the unperturbed hyperfine splitting of the $^{25}$Mg$^{+}$ $^{2}S_{1/2}$ ground electronic state, $ΔW / h = 1~788~762~752.85(13)$~Hz, with improved uncertainties. Both constants are relevant to the evaluation of the $^{27}$Al$^{+}$ quantum-logic clock systematic uncertainty. The measurement of $C_{2}$ is in agreement with a previous measurement and a new calculation at the $1~σ$ level. The measurement of $ΔW$ is in good agreement with a recent measurement and differs from a previously published result by approximately $2σ$. With the improved value for $ΔW$, we deduce an improved value for the nuclear-to-electronic g-factor ratio $g_{I}/g_{J} = 9.299 ~308 ~313(60) \times 10^{-5}$ and the nuclear g-factor for the $^{25}$Mg nucleus $g_{I} = 1.861 ~957 ~82(28) \times 10^{-4}$. Using the values of $C_{2}$ and $ΔW$ presented here, we derive a quadratic Zeeman shift of the $^{27}$Al$^{+}$ quantum-logic clock of $Δν/ ν= -(9241.8 \pm 3.7) \times 10^{-19}$, for a bias magnetic field of $B \approx 0.12$~mT.

physics.atom-ph↗

arXiv2019

An $^{27}$Al$^{+}$ quantum-logic clock with systematic uncertainty below $10^{-18}$

We describe an optical atomic clock based on quantum-logic spectroscopy of the $^1$S$_0$ $\leftrightarrow$ $^3$P$_0$ transition in $^{27}$Al$^{+}$ with a systematic uncertainty of ${9.4 \times 10^{-19}}$ and a frequency stability of ${1.2\times10^{-15}/\sqrtτ}$. A $^{25}$Mg$^{+}$ ion is simultaneously trapped with the $^{27}$Al$^{+}$ ion and used for sympathetic cooling and state readout. Improvements in a new trap have led to reduced secular motion heating, compared to previous $^{27}$Al$^{+}$ clocks, enabling clock operation with ion secular motion near the three-dimensional ground state. Operating the clock with a lower trap drive frequency has reduced excess micromotion compared to previous $^{27}$Al$^{+}$ clocks. Both of these improvements have led to a reduced time-dilation shift uncertainty. Other systematic uncertainties including those due to blackbody radiation and the second-order Zeeman effect have also been reduced.

physics.atom-ph↗

arXiv2017

Sympathetic ground state cooling and time-dilation shifts in an $^{27}\text{Al}^+$ optical clock

We report on Raman sideband cooling of ${^{25}\text{Mg}^+}$ to sympathetically cool the secular modes of motion in a $^{25}\text{Mg}^+$-$^{27}\!\text{Al}^+$ two-ion pair to near the three-dimensional (3D) ground state. The evolution of the Fock-state distribution during the cooling process is studied using a rate-equation simulation, and various heating sources that limit the efficiency of 3D sideband cooling in our system are discussed. We characterize the residual energy and heating rates of all of the secular modes of motion and estimate a secular motion time-dilation shift of ${-(1.9 \pm 0.1)\times 10^{-18}}$ for an ${^{27}\text{Al}^+}$ clock at a typical clock probe duration of $150$ ms. This is a 50-fold reduction in the secular motion time-dilation shift uncertainty in comparison with previous ${^{27}\text{Al}^+}$ clocks.

physics.atom-ph↗

arXiv2014

Scalable Spin Squeezing for Quantum-Enhanced Magnetometry with Bose-Einstein Condensates

A major challenge in quantum metrology is the generation of entangled states with macroscopic atom number. Here, we demonstrate experimentally that atomic squeezing generated via non-linear dynamics in Bose Einstein condensates, combined with suitable trap geometries, allows scaling to large ensemble sizes. We achieve a suppression of fluctuations by 5.3(5) dB for 12300 particles, which implies that similar squeezing can be achieved for more than 10$^7$ atoms. With this resource, we demonstrate quantum-enhanced magnetometry by swapping the squeezed state to magnetically sensitive hyperfine levels that have negligible nonlinearity. We find a quantum-enhanced single-shot sensitivity of 310(47) pT for static magnetic fields in a probe volume as small as 90 $μ$m$^3$.

quant-ph↗

arXiv2013

Accurate Atom Counting in Mesoscopic Ensembles

Many cold atom experiments rely on precise atom number detection, especially in the context of quantum-enhanced metrology where effects at the single particle level are important. Here, we investigate the limits of atom number counting via resonant fluorescence detection for mesoscopic samples of trapped atoms. We characterize the precision of these fluorescence measurements beginning from the single-atom level up to more than one thousand. By investigating the primary noise sources, we obtain single-atom resolution for atom numbers as high as 1200. This capability is an essential prerequisite for future experiments with highly entangled states of mesoscopic atomic ensembles.

physics.atom-ph↗

arXiv2011

Trapped-Ion State Detection through Coherent Motion

We demonstrate a general method for state detection of trapped ions that can be applied to a large class of atomic and molecular species. We couple a "spectroscopy" ion (Al+) to a "control" ion (Mg+) in the same trap and perform state detection through off-resonant laser excitation of the spectroscopy ion that induces coherent motion. The motional amplitude, dependent on the spectroscopy ion state, is measured either by time-resolved photon counting, or by resolved sideband excitations on the control ion. The first method provides a simplified way to distinguish "clock" states in Al+, which avoids ground state cooling and sideband transitions. The second method reduces spontaneous emission and optical pumping on the spectroscopy ion, which we demonstrate by nondestructively distinguishing Zeeman sublevels in the 1S0 ground state of Al+.

quant-ph↗

arXiv2011

Quantum coherence between two atoms beyond Q=10^15

We place two atoms in quantum superposition states and observe coherent phase evolution for 3.4x10^15 cycles. Correlation signals from the two atoms yield information about their relative phase even after the probe radiation has decohered. This technique was applied to a frequency comparison of two Al+ ions, where a fractional uncertainty of 3.7+1.0-0.8x10^-16/\sqrt{τ/s} was observed. Two measures of the Q-factor are reported: The Q-factor derived from quantum coherence is 3.4+2.4-1.1x10^16, and the spectroscopic Q-factor for a Ramsey time of 3 s is 6.7x10^15. As part of this experiment, we demonstrate a method to detect the individual quantum states of two Al+ ions in a Mg+-Al+-Al+ linear ion chain without spatially resolving the ions.

quant-ph↗

arXiv2010

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks

We have constructed an optical clock with a fractional frequency inaccuracy of 8.6e-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser-cool the Al+ ion and detect its quantum state. The frequency of the 1S0->3P0 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0e-18. The two clocks exhibit a relative stability of 2.8e-15/ sqrt(tau), and a fractional frequency difference of -1.8e-17, consistent with the accuracy limit of the older clock.

quant-ph↗

arXiv2009

Preparation of Dicke States in an Ion Chain

We have investigated theoretically and experimentally a method for preparing Dicke states in trapped atomic ions. We consider a linear chain of $N$ ion qubits that is prepared in a particular Fock state of motion, $|m>$. The $m$ phonons are removed by applying a laser pulse globally to the $N$ qubits, and converting the motional excitation to $m$ flipped spins. The global nature of this pulse ensures that the $m$ flipped spins are shared by all the target ions in a state that is a close approximation to the Dicke state $\D{N}{m}$. We calculate numerically the fidelity limits of the protocol and find small deviations from the ideal state for $m = 1$ and $m = 2$. We have demonstrated the basic features of this protocol by preparing the state $\D{2}{1}$ in two $^{25}$Mg$^+$ target ions trapped simultaneously with an $^{27}$Al$^+$ ancillary ion.

quant-ph↗

arXiv2007

High-fidelity, adaptive qubit measurements through repetitive information transfer

Using two trapped ion species ($\rm{^{27}Al^+}$ and $\rm{^9Be^+}$) as primary and ancillary systems, we implement qubit measurements based on the repetitive transfer of information and quantum nondemolition detection. The repetition provides a natural mechanism for an adaptive measurement strategy, which leads to exponentially lower error rates compared to using a fixed number of detection cycles. For a single qubit we demonstrate 99.94 % measurement fidelity. We also demonstrate a technique for adaptively measuring multiple qubit states using a single ancilla, and apply the technique to spectroscopy of an optical clock transition.

quant-ph↗

arXiv2007

Observation of the 1S0 - 3P0 clock transition in 27Al+

We report for the first time, laser spectroscopy of the 1S0 - 3P0 clock transition in 27Al+. A single aluminum ion and a single beryllium ion are simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb repulsion. This coupling allows the beryllium ion to sympathetically cool the aluminum ion, and also enables transfer of the aluminum's electronic state to the beryllium's hyperfine state, which can be measured with high fidelity. These techniques are applied to a measurement of the clock transition frequency, ν= 1 121 015 393 207 851(8) Hz. They are also used to measure the lifetime of the metastable clock state, τ= 20.6 +/- 1.4 s, the ground state 1S0 g-factor, g_S = -0.00079248(14), and the excited state 3P0 g-factor, g_P = -0.00197686(21), in units of the Bohr magneton.

physics.atom-ph↗

arXiv2006

Blackbody radiation shift of the 27Al+ 1S0 - 3P0 transition

The differential polarizability, due to near-infrared light at 1126 nm, of the 27Al+ 1S0 -> 3P0 clock transition is measured to be 4πε_0 x (1.6 +/- 0.5) x 10^{-31} m^3. This measurement is combined with experimental oscillator strengths to extrapolate the differential static polarizability of the clock transition as 4πε_0 x (1.5 +/- 0.5) x 10^{-31} m^3. The resulting room temperature blackbody fractional frequency shift of -8(3) x 10^{-18} is the lowest known shift of all atomic transitions under consideration for optical frequency standards. A method is presented to estimate the differential static polarizability of an optical transition, from a differential light shift measurement.

physics.atom-ph↗

arXiv2006

A microfabricated surface-electrode ion trap for scalable quantum information processing

We demonstrate confinement of individual atomic ions in a radio-frequency Paul trap with a novel geometry where the electrodes are located in a single plane and the ions confined above this plane. This device is realized with a relatively simple fabrication procedure and has important implications for quantum state manipulation and quantum information processing using large numbers of ions. We confine laser-cooled Mg-24 ions approximately 40 micrometer above planar gold electrodes. We measure the ions' motional frequencies and compare them to simulations. From measurements of the escape time of ions from the trap, we also determine a heating rate of approximately five motional quanta per millisecond for a trap frequency of 5.3 MHz.

quant-ph↗

arXiv2005

Long-lived qubit memory using atomic ions

We demonstrate experimentally a robust quantum memory using a magnetic-field-independent hyperfine transition in 9Be+ atomic ion qubits at a magnetic field B ~= 0.01194 T. We observe that the single physical qubit memory coherence time is greater than 10 seconds, an improvement of approximately five orders of magnitude from previous experiments with 9Be+. We also observe long coherence times of decoherence-free subspace logical qubits comprising two entangled physical qubits and discuss the merits of each type of qubit.

quant-ph↗