arXiv subjects

Nitzan Akerman

Publications and source records attributed to Nitzan Akerman.

53 records · Page 3Linked to original sources

arXiv2017

Experimental apparatus for overlapping a ground-state cooled ion with ultracold atoms

Experimental realizations of charged ions and neutral atoms in overlapping traps are gaining increasing interest due to their wide research application ranging from chemistry at the quantum level to quantum simulations of solid-state systems. Here, we describe a system in which we overlap a single ground-state cooled ion trapped in a linear Paul trap with a cloud of ultracold atoms such that both constituents are in the $μ$K regime. Excess micromotion (EMM) currently limits atom-ion interaction energy to the mK energy scale and above. We demonstrate spectroscopy methods and compensation techniques which characterize and reduce the ion's parasitic EMM energy to the $μ$K regime even for ion crystals of several ions. We give a substantial review on the non-equilibrium dynamics which governs atom-ion systems. The non-equilibrium dynamics is manifested by a power-law distribution of the ion's energy. We overview the coherent and non-coherent thermometry tools which we used to characterize the ion's energy distribution after single to many atom-ion collisions.

quant-ph↗

arXiv2017

Doppler cooling thermometry of a multi-level ion in the presence of micromotion

We study the time-dependent fluorescence of an initially hot, multi-level, single atomic ion trapped in a radio-frequency Paul trap during Doppler cooling. We have developed an analytical model that describes the fluorescence dynamics during Doppler cooling which is used to extract the initial energy of the ion. While previous models of Doppler cooling thermometry were limited to atoms with a two-level energy structure and neglected the effect of the trap oscillating electric fields, our model applies to atoms with multi-level energy structure and takes into account the influence of micromotion on the cooling dynamics. This thermometry applies to any initial energy distribution. We experimentally test our model with an ion prepared in a coherent, thermal and Tsallis energy distributions.

physics.atom-ph↗

arXiv2016

Trapping of molecular Oxygen together with Lithium atoms

We demonstrate simultaneous deceleration and trapping of a cold atomic and molecular mixture. This is the first step towards studies of cold atom-molecule collisions at low temperatures as well as application of sympathetic cooling. Both atoms and molecules are cooled in a supersonic expansion and are loaded into a moving magnetic trap which brings them to rest via the Zeeman interaction from an initial velocity of 375 m/s. We use a beam seeded with molecular Oxygen, and entrain it with Lithium atoms by laser ablation prior to deceleration. The deceleration ends with loading of the mixture into a static quadrupole trap, which is generated by two permanent magnets. We estimate $10^9$ trapped O$_2$ molecules and $10^5$ Li atoms with background pressure limited lifetime on the order of 1 second. With further improvements to Lithium entrainment we expect that sympathetic cooling of molecules is within reach.

physics.atom-ph↗

arXiv2016

Molecular beam brightening by shock-wave suppression

Supersonic beams are a prevalent source of cold molecules utilized in the study of chemical reactions, atom interferometry, gas-surface interactions, precision spectroscopy, molecular cooling and more. The triumph of this method emanates from the high densities produced in relation to other methods, however beam density remains fundamentally limited by interference with shock waves reflected from collimating surfaces. Here we show experimentally that this shock interaction can be reduced or even eliminated by cryo-cooling the interacting surface. An increase in beam density of nearly an order of magnitude was measured at the lowest surface temperature, with no further fundamental limitation reached. Visualization of the shock waves by plasma discharge and reproduction with direct simulation Monte Carlo calculations both indicate that the suppression of the shock structure is partially caused by lowering the momentum flux of reflected particles, and significantly enhanced by the adsorption of particles to the surface. We observe that the scaling of beam density with source pressure is recovered, paving the way to order of magnitude brighter cold molecular beams.

physics.atom-ph↗

arXiv2016

Dynamics of a ground-state cooled ion colliding with ultra-cold atoms

Ultra-cold atom-ion mixtures are gaining increasing interest due to their potential applications in quantum chemistry, quantum computing and many-body physics. Here, we studied the dynamics of a single ground-state cooled ion during few, to many, Langevin (spiraling) collisions with ultra-cold atoms. We measured the ion's energy distribution and observed a clear deviation from Maxwell-Boltzmann to a Tsallis characterized by a power-law tail of high energies. Unlike previous experiments, the energy scale of atom-ion interactions is not determined by either the atomic cloud temperature or the ion's trap residual excess-micromotion energy. Instead, it is determined by the force the atom exerts on the ion during a collision which is then amplified by the trap dynamics. This effect is intrinsic to ion Paul traps and sets the lower bound of atom-ion steady-state interaction energy in these systems. Despite the fact that our system is eventually driven out of the ultra-cold regime, we are capable of studying quantum effects by limiting the interaction to the first collision.

physics.atom-ph↗

arXiv2015

Atomic Quadrupole Moment Measurement Using Dynamic Decoupling

We present a method that uses dynamic decoupling of a multi-level quantum probe to distinguish small frequency shifts that depend on $m^2_{j}$, where $m^2_{j}$ is the angular momentum of level $\left|j\right\rangle$ along the quantization axis, from large noisy shifts that are linear in $m_{j}$, such as those due to magnetic field noise. Using this method we measured the electric quadrupole moment of the $4D_{\frac{5}{2}}$ level in $^{88}Sr^{+}$ to be $2.973^{+0.026}_{-0.033}\, ea_{0}^{2}$. Our measurement improves the uncertainty of this value by an order of magnitude and thus helps mitigate an important systematic uncertainty in $^{88}Sr^{+}$ based optical atomic clocks and verifies complicated many-body quantum calculations.

quant-ph↗

arXiv2015

Universal gate-set for trapped-ion qubits using a narrow linewidth diode laser

We report on the implementation of a high fidelity universal gate-set on optical qubits based on trapped $^{88}$Sr$^+$ ions for the purpose of quantum information processing. All coherent operations were performed using a narrow linewidth diode laser. We employed a master-slave configuration for the laser, where an ultra low expansion glass (ULE) Fabry-Perot cavity is used as a stable reference as well as a spectral filter. We characterized the laser spectrum using the ions with a modified Ramsey sequence which eliminated the affect of the magnetic field noise. We demonstrated high fidelity single qubit gates with individual addressing, based on inhomogeneous micromotion, on a two-ion chain as well as the Mølmer-Sørensen two-qubit entangling gate.

quant-ph↗

arXiv2013

Measurement of the magnetic interaction between two electrons

Electrons have an intrinsic, indivisible, magnetic dipole aligned with their internal angular momentum (spin). The magnetic interaction between two electrons can therefore impose a change in their spin orientation. This process, however, was never observed in experiment. The challenge is two-fold. At the atomic scale, where the coupling is relatively large, the magnetic interaction is often overshadowed by the much larger coulomb exchange counterpart. In typical situations where exchange is negligible, magnetic interactions are also very weak and well below ambient magnetic noise. Here we report on the first measurement of the magnetic interaction between two electronic spins. To this end, we used the ground state valence electrons of two $^{88}$Sr$^+$ ions, co-trapped in an electric Paul trap and separated by more than two micrometers. We measured the weak, millihertz scale (alternatively $10^{-18}$ eV or $10^{-14}$ K), magnetic interaction between their electronic spins. This, in the presence of magnetic noise that was six orders of magnitude larger than the respective magnetic fields the electrons apply on each other. Cooperative spin dynamics was kept coherent for 15 s during which spin-entanglement was generated. The sensitivity necessary for this measurement was provided by restricting the spin evolution to a Decoherence-Free Subspace (DFS) which is immune to collective magnetic field noise. Finally, by varying the separation between the two ions, we were able to recover the inverse cubic distance dependence of the interaction. The reported method suggests an alternative route to the search of long-range anomalous spin-spin forces and can be generalized to include Quantum Error Correction codes for other cases of extremely weak signal detection.

quant-ph↗

arXiv2013

Quantum Process Tomography of a Molmer-Sorensen Interaction

We report the quantum process tomography of a M$ø$lmer-S$ø$rensen entangling gate. The tomographic protocol relies on a single discriminatory transition, exploiting excess micromotion in the trap to realize all operations required to prepare all input states and analyze all output states. Using a master-slave diode lasers setup, we demonstrate a two-qubit entangling gate, with a fidelity of Bell state production of 0.985(10). We characterize its $χ$-process matrix, the simplest for an entanglement gate on a separable-states basis, and we observe that the dominant source of error is accurately modelled by a quantum depolarization channel.

quant-ph↗

arXiv2013

Addressing Two-Level Systems Variably Coupled to an Oscillating Field

We propose a simple method to spectrally resolve single-spins in a cold atomic system, thus realizing single-spin addressing. This scheme uses a dressing field with a spatially-dependent coupling to the atoms. We realize this scheme experimentally using a linear chain of trapped ions that are separated by $\sim3$ $μ$m, dressed by a laser field that is resonant with the micromotion sideband of a narrow optical transition.

quant-ph↗

arXiv2012

Reversal of Photon-Scattering Errors in Atomic Qubits

Spontaneous photon scattering by an atomic qubit is a notable example of environment-induced error and is a fundamental limit to the fidelity of quantum operations. In the scattering process the qubit loses its distinctive and coherent character owing to its entanglement with the photon. Using a single trapped ion we show that by utilizing the information carried by the photon we are able to coherently reverse this process and correct for the scattering error. We further used quantum process tomography to characterize the photon-scattering error and its correction scheme and demonstrate a correction fidelity greater than 85% whenever a photon was measured.

quant-ph↗

arXiv2012

Single-Spin Spectrum-Analyzer for a Strongly Coupled Environment

A qubit can be used as a sensitive spectrum analyzer of its environment. Here we show how the problem of spectral analysis of noise induced by a strongly coupled environment can be solved for discrete spectra. Our analytical model shows non-linear signal dependence on noise power, as well as possible frequency mixing, both are inherent to quantum evolution. This model enabled us to use a single trapped ion as a sensitive probe for strong, non-Gaussian, discrete magnetic field noise. To overcome ambiguities arising from the non-linear character of strong noise, we develop a three step noise characterization scheme: peak identification, magnitude identification and fine-tuning. Finally, we compare experimentally equidistant versus Uhrig pulse schemes for spectral analysis. The method is readily available to any quantum probe which can be coherently manipulated.

quant-ph↗

arXiv2012

Emergence of a measurement basis in atom-photon scattering

The process of quantum measurement has been a long standing source of debate. A measurement is postulated to collapse a wavefunction onto one of the states of a predetermined set - the measurement basis. This basis origin is not specified within quantum mechanics. According to the theory of decohernce, a measurement basis is singled out by the nature of coupling of a quantum system to its environment. Here we show how a measurement basis emerges in the evolution of the electronic spin of a single trapped atomic ion due to spontaneous photon scattering. Using quantum process tomography we visualize the projection of all spin directions, onto this basis, as a photon is scattered. These basis spin states are found to be aligned with the scattered photon propagation direction. In accordance with decohernce theory, they are subjected to a minimal increase in entropy due to the photon scattering, while, orthogonal states become fully mixed and their entropy is maximally increased. Moreover, we show that detection of the scattered photon polarization measures the spin state of the ion, in the emerging basis, with high fidelity. Lastly, we show that while photon scattering entangles all superpositions of pointer states with the scattered photon polarization, the measurement-basis states themselves remain classically correlated with it. Our findings show that photon scattering by atomic spin superpositions fulfils all the requirements from a quantum measurement process.

quant-ph↗

arXiv2011

Quantum control of $^{88}$Sr$^+$ in a miniature linear Paul trap

We report on the construction and characterization of an apparatus for quantum information experiments using $^{88}$Sr$^+$ ions. A miniature linear radio-frequency (rf) Paul trap was designed and built. Trap frequencies above 1 MHz in all directions are obtained with 50 V on the trap end-caps and less than 1 W of rf power. We encode a quantum bit (qubit) in the two spin states of the $S_{1/2}$ electronic ground-state of the ion. We constructed all the necessary laser sources for laser cooling and full coherent manipulation of the ions' external and internal states. Oscillating magnetic fields are used for coherent spin rotations. High-fidelity readout as well as a coherence time of 2.5 ms are demonstrated. Following resolved sideband cooling the average axial vibrational quanta of a single trapped ion is $\bar n=0.05$ and a heating rate of $\dot{\bar n}=0.016$ ms$^{-1}$ is measured.

quant-ph↗

arXiv2011

High-fidelity state detection and tomography of a single ion Zeeman qubit

We demonstrate high-fidelity Zeeman qubit state detection in a single trapped 88 Sr+ ion. Qubit readout is performed by shelving one of the qubit states to a metastable level using a narrow linewidth diode laser at 674 nm followed by state-selective fluorescence detection. The average fidelity reached for the readout of the qubit state is 0.9989(1). We then measure the fidelity of state tomography, averaged over all possible single-qubit states, which is 0.9979(2). We also fully characterize the detection process using quantum process tomography. This readout fidelity is compatible with recent estimates of the detection error-threshold required for fault-tolerant computation, whereas high-fidelity state tomography opens the way for high-precision quantum process tomography.

quant-ph↗

arXiv2011

Single Ion Quantum Lock-In Amplifier

We report on the implementation of a quantum analog to the classical lock-in amplifier. All the lock-in operations: modulation, detection and mixing, are performed via the application of non-commuting quantum operators on the electronic spin state of a single trapped Sr+ ion. We significantly increase its sensitivity to external fields while extending phase coherence by three orders of magnitude, to more than one second. With this technique we measure magnetic fields with sensitivity of 25 pT/sqrt(Hz) and light shifts with an uncertainty below 140 mHz after 1320 seconds of averaging. These sensitivities are limited by quantum projection noise and, to our knowledge, are more than two orders of magnitude better than with other single-spin probe technologies. In fact, our reported sensitivity is sufficient for the measurement of parity non-conservation, as well as the detection of the magnetic field of a single electronic-spin one micrometer from an ion-detector with nanometer resolution. As a first application we perform light shift spectroscopy of a narrow optical quadruple transition. Finally, we emphasize that the quantum lock-in technique is generic and can potentially enhance the sensitivity of any quantum sensor.

quant-ph↗

arXiv2010

A single-ion nonlinear mechanical oscillator

We study the steady state motion of a single trapped ion oscillator driven to the nonlinear regime. Damping is achieved via Doppler laser-cooling. The ion motion is found to be well described by the Duffing oscillator model with an additional nonlinear damping term. We demonstrate a unique ability of tuning both the linear as well as the nonlinear damping coefficients by controlling the cooling laser parameters. Our observations open a way for the investigation of nonlinear dynamics on the quantum-to-classical interface as well as mechanical noise squeezing in laser-cooling dynamics.

quant-ph↗