arXiv subjects

D. J. Wineland

Publications and source records attributed to D. J. Wineland.

At least 73 records · Page 4Linked to original sources

arXiv2008

Trapped-ion quantum logic gates based on oscillating magnetic fields

Oscillating magnetic fields and field gradients can be used to implement single-qubit rotations and entangling multi-qubit quantum gates for trapped-ion quantum information processing (QIP). With fields generated by currents in microfabricated surface-electrode traps, it should be possible to achieve gate speeds that are comparable to those of optically induced gates for realistic distances between the ion crystal and the electrode surface. Magnetic-field-mediated gates have the potential to significantly reduce the overhead in laser beam control and motional state initialization compared to current QIP experiments with trapped ions and will eliminate spontaneous scattering, a fundamental source of decoherence in laser-mediated gates.

quant-ph↗

arXiv2007

Passive Cooling of a Micromechanical Oscillator with a Resonant Electric Circuit

We cool the fundamental mode of a miniature cantilever by capacitively coupling it to a driven rf resonant circuit. Cooling results from the rf capacitive force, which is phase shifted relative to the cantilever motion. We demonstrate the technique by cooling a 7 kHz cantilever from room temperature to 45 K, obtaining reasonable agreement with a model for the cooling, damping, and frequency shift. Extending the method to higher frequencies in a cryogenic system could enable ground state cooling and may prove simpler than related optical experiments in a low temperature apparatus.

cond-mat.other↗

arXiv2007

Transport quantum logic gates for trapped ions

Many efforts are currently underway to build a device capable of large scale quantum information processing (QIP). Whereas QIP has been demonstrated for a few qubits in several systems, many technical difficulties must be overcome in order to construct a large-scale device. In one proposal for large-scale QIP, trapped ions are manipulated by precisely controlled light pulses and moved through and stored in multizone trap arrays. The technical overhead necessary to precisely control both the ion geometrical configurations and the laser interactions is demanding. Here we propose methods that significantly reduce the overhead on laser beam control for performing single and multiple qubit operations on trapped ions. We show how a universal set of operations can be implemented by controlled transport of ions through stationary laser beams. At the same time, each laser beam can be used to perform many operations in parallel, potentially reducing the total laser power necessary to carry out QIP tasks. The overall setup necessary for implementing transport gates is simpler than for gates executed on stationary ions. We also suggest a transport-based two-qubit gate scheme utilizing microfabricated permanent magnets that can be executed without laser light.

quant-ph↗

arXiv2007

Simplified motional heating rate measurements of trapped ions

We have measured motional heating rates of trapped atomic ions, a factor that can influence multi-ion quantum logic gate fidelities. Two simplified techniques were developed for this purpose: one relies on Raman sideband detection implemented with a single laser source, while the second is even simpler and is based on time-resolved fluorescence detection during Doppler recooling. We applied these methods to determine heating rates in a microfrabricated surface-electrode trap made of gold on fused quartz, which traps ions 40 microns above its surface. Heating rates obtained from the two techniques were found to be in reasonable agreement. In addition, the trap gives rise to a heating rate of 300 plus or minus 30 per second for a motional frequency of 5.25 MHz, substantially below the trend observed in other traps.

quant-ph↗

arXiv2007

Fluorescence during Doppler cooling of a single trapped atom

We investigate the temporal dynamics of Doppler cooling of an initially hot single trapped atom in the weak binding regime using a semiclassical approach. We develop an analytical model for the simplest case of a single vibrational mode for a harmonic trap, and show how this model allows us to estimate the initial energy of the trapped particle by observing the fluorescence rate during the cooling process. The experimental implementation of this temperature measurement provides a way to measure atom heating rates by observing the temperature rise in the absence of cooling. This method is technically relatively simple compared to conventional sideband detection methods, and the two methods are in reasonable agreement. We also discuss the effects of RF micromotion, relevant for a trapped atomic ion, and the effect of coupling between the vibrational modes on the cooling dynamics.

quant-ph↗

arXiv2007

Randomized Benchmarking of Quantum Gates

A key requirement for scalable quantum computing is that elementary quantum gates can be implemented with sufficiently low error. One method for determining the error behavior of a gate implementation is to perform process tomography. However, standard process tomography is limited by errors in state preparation, measurement and one-qubit gates. It suffers from inefficient scaling with number of qubits and does not detect adverse error-compounding when gates are composed in long sequences. An additional problem is due to the fact that desirable error probabilities for scalable quantum computing are of the order of 0.0001 or lower. Experimentally proving such low errors is challenging. We describe a randomized benchmarking method that yields estimates of the computationally relevant errors without relying on accurate state preparation and measurement. Since it involves long sequences of randomly chosen gates, it also verifies that error behavior is stable when used in long computations. We implemented randomized benchmarking on trapped atomic ion qubits, establishing a one-qubit error probability per randomized pi/2 pulse of 0.00482(17) in a particular experiment. We expect this error probability to be readily improved with straightforward technical modifications.

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↗

arXiv2007

Errors in trapped-ion quantum gates due to spontaneous photon scattering

We analyze the error in trapped-ion, hyperfine qubit, quantum gates due to spontaneous scattering of photons from the gate laser beams. We investigate single-qubit rotations that are based on stimulated Raman transitions and two-qubit entangling phase-gates that are based on spin-dependent optical dipole forces. This error is compared between different ion species currently being investigated as possible quantum information carriers. For both gate types we show that with realistic laser powers the scattering error can be reduced to below current estimates of the fault-tolerance error threshold.

quant-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

Transport dynamics of single ions in segmented microstructured Paul trap arrays

It was recently proposed to use small groups of trapped ions as qubit carriers in miniaturized electrode arrays that comprise a large number of individual trapping zones, between which ions could be moved. This approach might be scalable for quantum information processing with a large numbers of qubits. Processing of quantum information is achieved by transporting ions to and from separate memory and qubit manipulation zones in between quantum logic operations. The transport of ion groups in this scheme plays a major role and requires precise experimental control and fast transport. In this paper we introduce a theoretical framework to study ion transport in external potentials that might be created by typical miniaturized Paul trap electrode arrays. In particular we discuss the relationship between classical and quantum descriptions of the transport and study the energy transfer to the oscillatory motion during near-adiabatic transport. Based on our findings we suggest a numerical method to find electrode potentials as a function of time to optimize the local potential an ion experiences during transport. We demonstrate this method for one specific electrode geometry that should closely represent the situation encountered in realistic trap arrays.

quant-ph↗

arXiv2006

Cantilever cooling with radio frequency circuits

We consider a method to reduce the kinetic energy in a low-order mode of a miniature cantilever. If the cantilever contributes to the capacitance of a driven RF circuit, a force on the cantilever exists due to the electric field energy stored in the capacitance. If this force acts with an appropriate phase shift relative to the motion of the cantilever, it can oppose the velocity of the cantilever, leading to cooling. Such cooling may enable reaching the quantum regime of cantilever motion.

quant-ph↗

arXiv2006

A microfabricated surface-electrode ion trap in silicon

The prospect of building a quantum information processor underlies many recent advances ion trap fabrication techniques. Potentially, a quantum computer could be constructed from a large array of interconnected ion traps. We report on a micrometer-scale ion trap, fabricated from bulk silicon using micro-electromechanical systems (MEMS) techniques. The trap geometry is relatively simple in that the electrodes lie in a single plane beneath the ions. In such a trap we confine laser-cooled 24Mg+ ions approximately 40 microns above the surface. The fabrication technique and planar electrode geometry together make this approach amenable to scaling up to large trap arrays. In addition we observe that little laser cooling light is scattered by the electrodes.

quant-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

Quantum control, quantum information processing, and quantum-limited metrology with trapped ions

We briefly discuss recent experiments on quantum information processing using trapped ions at NIST. A central theme of this work has been to increase our capabilities in terms of quantum computing protocols, but we have also applied the same concepts to improved metrology, particularly in the area of frequency standards and atomic clocks. Such work may eventually shed light on more fundamental issues, such as the quantum measurement problem.

quant-ph↗

arXiv2005

Surface-Electrode Architecture for Ion-Trap Quantum Information Processing

We investigate a surface-mounted electrode geometry for miniature linear radio frequency Paul ion traps. The electrodes reside in a single plane on a substrate, and the pseudopotential minimum of the trap is located above the substrate at a distance on order of the electrodes' lateral extent or separation. This architecture provides the possibility to apply standard microfabrication principles to the construction of multiplexed ion traps, which may be of particular importance in light of recent proposals for large-scale quantum computation based on individual trapped ions.

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↗

arXiv2005

Hyperfine Coherence in the Presence of Spontaneous Photon Scattering

The coherence of a hyperfine-state superposition of a trapped $^{9}$Be$^+$ ion in the presence of off-resonant light is experimentally studied. It is shown that Rayleigh elastic scattering of photons that does not change state populations also does not affect coherence. Coherence times exceeding the average scattering time of 19 photons are observed. This result implies that, with sufficient control over its parameters, laser light can be used to manipulate hyperfine-state superpositions with very little decoherence.

quant-ph↗