Xianli Zhang - Academia.edu (original) (raw)

Papers by Xianli Zhang

Journal of Physics: Conference Series, 2011

Experiments performed within the last year have demonstrated Rydberg state mediated quantum gates... more Experiments performed within the last year have demonstrated Rydberg state mediated quantum gates and deterministic entanglement between pairs of trapped neutral atoms. These experiments validate ten year old proposals for Rydberg mediated quantum logic, but are only the beginning of ongoing efforts to improve the fidelity of the results obtained and scale the experiments to larger numbers of qubits. We present here a summary of the results to date, along with a critical evaluation of the prospects for higher fidelity Rydberg gates.

Physical Review A

Accurate measurements of optical line broadening and microwave hyperfine transition shifts are es... more Accurate measurements of optical line broadening and microwave hyperfine transition shifts are essential for optimizing the performance of buffer-gas atomic clocks. Previous literature has reported inconsistent measurement values. We report measurements of the D 1 transition broadening and hyperfine frequency shift coefficients for 87 Rb and 133 Cs due to collisions with Ne and Ar atoms, as well as N 2 molecules which is commonly employed for quenching in gas cell atomic clocks.

AIP Conference Proceedings

We develop a projection imaging technique to study ultracold plasma dynamics. We image the charge... more We develop a projection imaging technique to study ultracold plasma dynamics. We image the charged particle spatial distributions by extraction with a high-voltage pulse onto a position-sensitive detector. Measuring the 2D width of the ion image at later times (the ion image size in the first 20 µs is dominated by the Coulomb explosion of the dense ion cloud), we extract the plasma expansion velocity. These velocities at different initial electron temperatures match earlier results obtained by measuring the plasma oscillation frequency. The electron image size slowly decreases during the plasma lifetime because of the strong Coulomb force of the ion cloud on the electrons, electron loss and Coulomb explosion effects.

We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We... more We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We use a time-of-flight projection imaging method to extract the ion distribution at varying times during the plasma evolution. Our previous study showed the transverse expansion velocity in a uniform longitudinal magnetic field scales as B-1/2 for fields up to 70 G, explained

Physical Review Letters, 2015

We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed ... more We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed by an optical lattice. Addressing is accomplished using rapidly reconfigurable crossed laser beams to selectively ac Stark shift target atoms, so that only target atoms are resonant with state-changing microwaves. The effect of these targeted single qubit gates on the quantum information stored in non-targeted atoms is smaller than 3×10-3 in state fidelity. This is an important step along the path of converting the scalability promise of neutral atoms into reality. Trapped neutral atoms possess the essential features of a qubit: 1 their internal states can be initialized and measured, they have long coherence times, 2 and they can be entangled. 3, 4

ABSTRACT Despite being an important collisional process in cold plasmas, three-body recombination... more ABSTRACT Despite being an important collisional process in cold plasmas, three-body recombination (3BR) is described by a rate expression that has yet to be strongly confirmed for very low electron temperatures. While the low temperature 3BR rates have recently been measured in an ultracold plasma, the strong temperature dependence (T-9/2) of the 3BR rate expression, combined with the difficulty of accurately measuring electron temperatures of ultracold plasmas, makes it difficult to verify the 3BR rate expressions at low temperatures. In this work, we use microwave ionization to measure the Rydberg population distributions in an ultracold plasma in an attempt to test the predictions of 3BR rate theory. This method of testing 3BR rate equations has a clear advantage over measuring the overall 3BR rate, as it is far less dependent on the particular electron temperature of the plasma.

ABSTRACT We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to ... more ABSTRACT We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We use a time-of-flight projection imaging method to extract the ion distribution at varying times during the plasma evolution. Our previous study showed the transverse expansion velocity in a uniform longitudinal magnetic field scales as B-1/2 for fields up to 70 G, explained by a nonlinear ambipolar diffusion model that involves anisotropic diffusion in two directions. Preliminary results show above 100 G and up to 500 G, the expansion velocity does not continue to decrease, but levels off at ˜10m/s. This limit corresponds to the ion thermal velocity at an ion temperature of 1 K. We also observe a flat top in the ion images that we attribute to the formation of a shockwave at the edge of the ion cloud during the time of flight to the detector. This work is a preliminary step in pursuing 3D magnetic confinement of the ultracold plasma. This work is partially supported by the NSF.

ABSTRACT Deterministic preparation of single atom occupancy in optical traps is an important prer... more ABSTRACT Deterministic preparation of single atom occupancy in optical traps is an important prerequisite for implementation of neutral atom quantum computing. We present experimental progress towards that goal using Rydberg blockade interactions of cold Rb atoms. Starting with 5-15 atoms in an optical trap a sequence of optical pulses that implement Rydberg blockade dynamics is used to remove all but one of the atoms. We demonstrate single atom preparation with > 55% probability and discuss factors limiting the current performance.

Journal of Physics: Conference Series, 2011

Experiments performed within the last year have demonstrated Rydberg state mediated quantum gates... more Experiments performed within the last year have demonstrated Rydberg state mediated quantum gates and deterministic entanglement between pairs of trapped neutral atoms. These experiments validate ten year old proposals for Rydberg mediated quantum logic, but are only the beginning of ongoing efforts to improve the fidelity of the results obtained and scale the experiments to larger numbers of qubits. We present here a summary of the results to date, along with a critical evaluation of the prospects for higher fidelity Rydberg gates.

Physical Review A

Accurate measurements of optical line broadening and microwave hyperfine transition shifts are es... more Accurate measurements of optical line broadening and microwave hyperfine transition shifts are essential for optimizing the performance of buffer-gas atomic clocks. Previous literature has reported inconsistent measurement values. We report measurements of the D 1 transition broadening and hyperfine frequency shift coefficients for 87 Rb and 133 Cs due to collisions with Ne and Ar atoms, as well as N 2 molecules which is commonly employed for quenching in gas cell atomic clocks.

AIP Conference Proceedings

We develop a projection imaging technique to study ultracold plasma dynamics. We image the charge... more We develop a projection imaging technique to study ultracold plasma dynamics. We image the charged particle spatial distributions by extraction with a high-voltage pulse onto a position-sensitive detector. Measuring the 2D width of the ion image at later times (the ion image size in the first 20 µs is dominated by the Coulomb explosion of the dense ion cloud), we extract the plasma expansion velocity. These velocities at different initial electron temperatures match earlier results obtained by measuring the plasma oscillation frequency. The electron image size slowly decreases during the plasma lifetime because of the strong Coulomb force of the ion cloud on the electrons, electron loss and Coulomb explosion effects.

We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We... more We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We use a time-of-flight projection imaging method to extract the ion distribution at varying times during the plasma evolution. Our previous study showed the transverse expansion velocity in a uniform longitudinal magnetic field scales as B-1/2 for fields up to 70 G, explained

Physical Review Letters, 2015

We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed ... more We demonstrate arbitrary coherent addressing of individual neutral atoms in a 5×5×5 array formed by an optical lattice. Addressing is accomplished using rapidly reconfigurable crossed laser beams to selectively ac Stark shift target atoms, so that only target atoms are resonant with state-changing microwaves. The effect of these targeted single qubit gates on the quantum information stored in non-targeted atoms is smaller than 3×10-3 in state fidelity. This is an important step along the path of converting the scalability promise of neutral atoms into reality. Trapped neutral atoms possess the essential features of a qubit: 1 their internal states can be initialized and measured, they have long coherence times, 2 and they can be entangled. 3, 4

ABSTRACT Despite being an important collisional process in cold plasmas, three-body recombination... more ABSTRACT Despite being an important collisional process in cold plasmas, three-body recombination (3BR) is described by a rate expression that has yet to be strongly confirmed for very low electron temperatures. While the low temperature 3BR rates have recently been measured in an ultracold plasma, the strong temperature dependence (T-9/2) of the 3BR rate expression, combined with the difficulty of accurately measuring electron temperatures of ultracold plasmas, makes it difficult to verify the 3BR rate expressions at low temperatures. In this work, we use microwave ionization to measure the Rydberg population distributions in an ultracold plasma in an attempt to test the predictions of 3BR rate theory. This method of testing 3BR rate equations has a clear advantage over measuring the overall 3BR rate, as it is far less dependent on the particular electron temperature of the plasma.

ABSTRACT We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to ... more ABSTRACT We study the expansion dynamics of an ultracold plasma in uniform magnetic fields up to 500 G. We use a time-of-flight projection imaging method to extract the ion distribution at varying times during the plasma evolution. Our previous study showed the transverse expansion velocity in a uniform longitudinal magnetic field scales as B-1/2 for fields up to 70 G, explained by a nonlinear ambipolar diffusion model that involves anisotropic diffusion in two directions. Preliminary results show above 100 G and up to 500 G, the expansion velocity does not continue to decrease, but levels off at ˜10m/s. This limit corresponds to the ion thermal velocity at an ion temperature of 1 K. We also observe a flat top in the ion images that we attribute to the formation of a shockwave at the edge of the ion cloud during the time of flight to the detector. This work is a preliminary step in pursuing 3D magnetic confinement of the ultracold plasma. This work is partially supported by the NSF.

ABSTRACT Deterministic preparation of single atom occupancy in optical traps is an important prer... more ABSTRACT Deterministic preparation of single atom occupancy in optical traps is an important prerequisite for implementation of neutral atom quantum computing. We present experimental progress towards that goal using Rydberg blockade interactions of cold Rb atoms. Starting with 5-15 atoms in an optical trap a sequence of optical pulses that implement Rydberg blockade dynamics is used to remove all but one of the atoms. We demonstrate single atom preparation with > 55% probability and discuss factors limiting the current performance.