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Kenneth R Brown

Michael J. Fitzpatrick Distinguished Professor of Engineering
Electrical and Computer Engineering
701 W Main St, Suite 400, Durham, NC 27701

Selected Publications


Single-shot error correction on toric codes with high-weight stabilizers

Journal Article Physical Review A · May 1, 2024 For quantum error correction codes the required number of measurement rounds typically increases with the code distance when measurements are faulty. Single-shot error correction allows for an error threshold with only one round of noisy syndrome measureme ... Full text Cite

Optimization Tools for Distance-Preserving Flag Fault-Tolerant Error Correction

Journal Article PRX Quantum · April 1, 2024 Lookup-table decoding is fast and distance preserving, making it attractive for near-term quantum computer architectures with small-distance quantum error-correcting codes. In this work, we develop several optimization tools that can potentially reduce the ... Full text Cite

Trellis Decoding For Qudit Stabilizer Codes And Its Application To Qubit Topological Codes

Journal Article IEEE Transactions on Quantum Engineering · January 1, 2024 Trellis decoders are a general decoding technique first applied to qubit-based quantum error correction codes by Ollivier and Tillich in 2006. Here we improve the scalability and practicality of their theory, show that it has strong structure, extend the r ... Full text Cite

Quantum simulation of conical intersections using trapped ions.

Journal Article Nature chemistry · November 2023 Conical intersections often control the reaction products of photochemical processes and occur when two electronic potential energy surfaces intersect. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the g ... Full text Cite

Quantum Simulation of Polarized Light-Induced Electron Transfer with a Trapped-Ion Qutrit System.

Journal Article The journal of physical chemistry letters · July 2023 Electron transfer within and between molecules is crucial in chemistry, biochemistry, and energy science. This study describes a quantum simulation method that explores the influence of light polarization on electron transfer between two molecules. By impl ... Full text Cite

Adiabatically controlled motional states of a Formula Presented and Formula Presented trapped-ion chain cooled to the ground state

Journal Article Physical Review A · July 1, 2023 Control of the external degree of freedom of trapped molecular ions is essential for their promising applications to spectroscopy, precision measurements of fundamental constants, and quantum information technology. Here, we demonstrate near ground-state c ... Full text Cite

Quantum Error Correction with Metastable States of Trapped Ions Using Erasure Conversion

Journal Article PRX Quantum · April 1, 2023 Erasures, or errors with known locations, are a more favorable type of error for quantum error-correcting codes than Pauli errors. Converting physical noise into erasures can significantly improve the performance of quantum error correction. Here, we apply ... Full text Cite

Adaptive syndrome measurements for Shor-style error correction

Journal Article Quantum · January 1, 2023 The Shor fault-tolerant error correction (FTEC) scheme uses transversal gates and ancilla qubits prepared in the cat state in syndrome extraction circuits to prevent propagation of errors caused by gate faults. For a stabilizer code of distance d that can ... Full text Cite

Determination of Multimode Motional Quantum States in a Trapped Ion System.

Journal Article Physical review letters · September 2022 Trapped atomic ions are a versatile platform for studying interactions between spins and bosons by coupling the internal states of the ions to their motion. Measurement of complex motional states with multiple modes is challenging, because all motional sta ... Full text Cite

Single-shot error correction on toric codes with high-weight stabilizers

Journal Article Physical Review A · May 1, 2024 For quantum error correction codes the required number of measurement rounds typically increases with the code distance when measurements are faulty. Single-shot error correction allows for an error threshold with only one round of noisy syndrome measureme ... Full text Cite

Optimization Tools for Distance-Preserving Flag Fault-Tolerant Error Correction

Journal Article PRX Quantum · April 1, 2024 Lookup-table decoding is fast and distance preserving, making it attractive for near-term quantum computer architectures with small-distance quantum error-correcting codes. In this work, we develop several optimization tools that can potentially reduce the ... Full text Cite

Trellis Decoding For Qudit Stabilizer Codes And Its Application To Qubit Topological Codes

Journal Article IEEE Transactions on Quantum Engineering · January 1, 2024 Trellis decoders are a general decoding technique first applied to qubit-based quantum error correction codes by Ollivier and Tillich in 2006. Here we improve the scalability and practicality of their theory, show that it has strong structure, extend the r ... Full text Cite

Quantum simulation of conical intersections using trapped ions.

Journal Article Nature chemistry · November 2023 Conical intersections often control the reaction products of photochemical processes and occur when two electronic potential energy surfaces intersect. Theory predicts that the conical intersection will result in a geometric phase for a wavepacket on the g ... Full text Cite

Quantum Simulation of Polarized Light-Induced Electron Transfer with a Trapped-Ion Qutrit System.

Journal Article The journal of physical chemistry letters · July 2023 Electron transfer within and between molecules is crucial in chemistry, biochemistry, and energy science. This study describes a quantum simulation method that explores the influence of light polarization on electron transfer between two molecules. By impl ... Full text Cite

Adiabatically controlled motional states of a Formula Presented and Formula Presented trapped-ion chain cooled to the ground state

Journal Article Physical Review A · July 1, 2023 Control of the external degree of freedom of trapped molecular ions is essential for their promising applications to spectroscopy, precision measurements of fundamental constants, and quantum information technology. Here, we demonstrate near ground-state c ... Full text Cite

Quantum Error Correction with Metastable States of Trapped Ions Using Erasure Conversion

Journal Article PRX Quantum · April 1, 2023 Erasures, or errors with known locations, are a more favorable type of error for quantum error-correcting codes than Pauli errors. Converting physical noise into erasures can significantly improve the performance of quantum error correction. Here, we apply ... Full text Cite

Adaptive syndrome measurements for Shor-style error correction

Journal Article Quantum · January 1, 2023 The Shor fault-tolerant error correction (FTEC) scheme uses transversal gates and ancilla qubits prepared in the cat state in syndrome extraction circuits to prevent propagation of errors caused by gate faults. For a stabilizer code of distance d that can ... Full text Cite

Determination of Multimode Motional Quantum States in a Trapped Ion System.

Journal Article Physical review letters · September 2022 Trapped atomic ions are a versatile platform for studying interactions between spins and bosons by coupling the internal states of the ions to their motion. Measurement of complex motional states with multiple modes is challenging, because all motional sta ... Full text Cite

Hidden Inverses: Coherent Error Cancellation at the Circuit Level

Journal Article Physical Review Applied · March 1, 2022 Coherent gate errors are a concern in many proposed quantum-computing architectures. Here, we show that certain coherent errors can be reduced by a local optimization that chooses between two forms of the same Hermitian and unitary quantum gate. We refer t ... Full text Cite

Controlled preparation and vibrational excitation of single ultracold molecular hydrogen ions

Journal Article Molecular Physics · January 1, 2022 A single, trapped and ultracold molecular hydrogen ion is an attractive quantum system for exploring various aspects of fundamental physics, such as the determination of fundamental constants and testing their time-independence. Here we demonstrate, for th ... Full text Cite

Stable Turnkey Laser System for a Yb/Ba Trapped-Ion Quantum Computer

Journal Article IEEE Transactions on Quantum Engineering · January 1, 2022 This work presents a stable and reliable turnkey continuous-wave laser system for a Yb/Ba multispecies trapped-ion quantum computer. The compact and rack-mountable optics system exhibits high robustness, operating over a year without realignment, regardles ... Full text Cite

Materials challenges for trapped-ion quantum computers

Journal Article Nature Reviews Materials · October 1, 2021 Trapped-ion quantum information processors store information in atomic ions maintained in position in free space by electric fields. Quantum logic is enacted through manipulation of the ions’ internal and shared motional quantum states using optical and mi ... Full text Cite

Fault-tolerant control of an error-corrected qubit.

Journal Article Nature · October 2021 Quantum error correction protects fragile quantum information by encoding it into a larger quantum system1,2. These extra degrees of freedom enable the detection and correction of errors, but also increase the control complexity of the encoded l ... Full text Open Access Cite

Between Shor and Steane: A Unifying Construction for Measuring Error Syndromes.

Journal Article Physical review letters · August 2021 Fault-tolerant quantum error correction requires the measurement of error syndromes in a way that minimizes correlated errors on the quantum data. Steane and Shor ancilla are two well-known methods for fault-tolerant syndrome extraction. In this Letter, we ... Full text Cite

Constructions for measuring error syndromes in Calderbank-Shor-Steane codes between Shor and Steane methods

Journal Article Physical Review A · August 1, 2021 In another work [S. Huang and K. R. Brown, Phys. Rev. Lett. 127, 090505 (2021)10.1103/PhysRevLett.127.090505] we introduced syndrome extraction methods for Calderbank-Shor-Steane quantum error-correction codes that interpolate between the well-known Shor a ... Full text Cite

Demonstration of Shor Encoding on a Trapped-Ion Quantum Computer

Journal Article Physical Review Applied · August 1, 2021 Fault-tolerant quantum error correction (QEC) is crucial for unlocking the true power of quantum computers. QEC codes use multiple physical qubits to encode a logical qubit, which is protected against errors at the physical qubit level. Here, we use a trap ... Full text Cite

Hidden Inverses: Coherent Error Cancellation at the Circuit Level

Journal Article Phys. Rev. Applied · April 2, 2021 Coherent gate errors are a concern in many proposed quantum computing architectures. These errors can be effectively handled through composite pulse sequences for single-qubit gates, however, such techniques are less feasible for entangling operations. In ... Link to item Cite

Quantum Simulators: Architectures and Opportunities

Journal Article PRX Quantum · January 1, 2021 Quantum simulators are a promising technology on the spectrum of quantum devices from specialized quantum experiments to universal quantum computers. These quantum devices utilize entanglement and many-particle behavior to explore and solve hard scientific ... Full text Cite

Ground-state energy estimation of the water molecule on a trapped-ion quantum computer

Journal Article npj Quantum Information · December 1, 2020 Quantum computing leverages the quantum resources of superposition and entanglement to efficiently solve computational problems considered intractable for classical computers. Examples include calculating molecular and nuclear structure, simulating strongl ... Full text Cite

Improved Quantum Circuits via Intermediate Qutrits

Journal Article ACM Transactions on Quantum Computing · December 1, 2020 Quantum computation is traditionally expressed in terms of quantum bits, or qubits. In this work, we instead consider three-level qutrits. Past work with qutrits has demonstrated only constant factor improvements, owing to the log2(3) binary-to-ternary com ... Full text Cite

Extended flag gadgets for low-overhead circuit verification

Journal Article Physical Review A · November 10, 2020 Flag verification techniques are useful in quantum error correction for detecting critical faults. Here we present an application of flag-verification techniques for improving postselected performance of near-term algorithms. We extend the definition of wh ... Full text Cite

Critical faults of leakage errors on the surface code

Journal Article Proceedings - IEEE International Conference on Quantum Computing and Engineering, QCE 2020 · October 1, 2020 Leakage is a particularly damaging error that occurs when a qubit leaves the defined computational subspace. Leakage errors limit the effectiveness of quantum error correcting codes by spreading additional errors to other qubits and corrupting syndrome mea ... Full text Cite

High-Fidelity Two-Qubit Gates Using a Microelectromechanical-System-Based Beam Steering System for Individual Qubit Addressing.

Journal Article Physical review letters · October 2020 In a large scale trapped atomic ion quantum computer, high-fidelity two-qubit gates need to be extended over all qubits with individual control. We realize and characterize high-fidelity two-qubit gates in a system with up to four ions using radial modes. ... Full text Cite

Resource-Efficient Quantum Computing by Breaking Abstractions

Journal Article Proceedings of the IEEE · August 1, 2020 Building a quantum computer that surpasses the computational power of its classical counterpart is a great engineering challenge. Quantum software optimizations can provide an accelerated pathway to the first generation of quantum computing (QC) applicatio ... Full text Cite

Generating fault-tolerant cluster states from crystal structures

Journal Article Quantum · July 13, 2020 Measurement-based quantum computing (MBQC) is a promising alternative to traditional circuit-based quantum computing predicated on the construction and measurement of cluster states. Recent work has demonstrated that MBQC provides a more general framework ... Full text Cite

Logical performance of 9 qubit compass codes in ion traps with crosstalk errors

Journal Article Quantum Science and Technology · July 1, 2020 We simulate four quantum error correcting codes under error models inspired by realistic noise sources in near-term ion trap quantum computers: T 2 dephasing, gate overrotation, and crosstalk. We use this data to find preferred codes for given error parame ... Full text Cite

Fault-tolerant weighted union-find decoding on the toric code

Journal Article Physical Review A · July 1, 2020 Quantum error correction requires decoders that are both accurate and efficient. To this end, union-find decoding has emerged as a promising candidate for error correction on the surface code. In this work, we benchmark a weighted variant of the union-find ... Full text Cite

Fault-tolerant compass codes

Journal Article Physical Review A · April 1, 2020 We study a class of gauge fixings of the Bacon-Shor code at the circuit level, which includes a subfamily of generalized surface codes. We show that for these codes, fault tolerance can be achieved by direct measurements of the stabilizers. By simulating o ... Full text Cite

A hybrid ion-atom trap with integrated high resolution mass spectrometer

Journal Article Review of Scientific Instruments · October 1, 2019 In this article, we describe the design, construction, and implementation of our ion-atom hybrid system incorporating a high resolution time of flight mass spectrometer (TOFMS). Potassium atoms (39K) in a magneto optical trap and laser cooled calcium ions ... Full text Open Access Cite

Leakage mitigation for quantum error correction using a mixed qubit scheme

Journal Article Physical Review A · September 18, 2019 Leakage errors take qubits out of the computational subspace and will accumulate if not addressed. A leaked qubit will reduce the effectiveness of quantum error correction protocols due to the cost of implementing leakage reduction circuits and the harm ca ... Full text Cite

Two-qubit entangling gates within arbitrarily long chains of trapped ions

Journal Article Physical Review A · August 26, 2019 Ion trap quantum computers are based on modulating the Coulomb interaction between atomic ion qubits using external forces. However, the spectral crowding of collective motional modes could pose a challenge to the control of such interactions for large num ... Full text Open Access Cite

Handling leakage with subsystem codes

Journal Article New Journal of Physics · July 30, 2019 Leakage is a particularly damaging error that occurs when a qubit state falls out of its two-level computational subspace. Compared to independent depolarizing noise, leaked qubits may produce many more configurations of harmful correlated errors during er ... Full text Cite

Asymptotic improvements to quantum circuits via qutrits

Conference Proceedings - International Symposium on Computer Architecture · June 22, 2019 Quantum computation is traditionally expressed in terms of quantum bits, or qubits. In this work, we instead consider three-level qutrits. Past work with qutrits has demonstrated only constant factor improvements, owing to the log2(3) binary-to-ternary com ... Full text Cite

2D Compass Codes

Journal Article Physical Review X · May 29, 2019 The compass model on a square lattice provides a natural template for building subsystem stabilizer codes. The surface code and the Bacon-Shor code represent two extremes of possible codes depending on how many gauge qubits are fixed. We explore threshold ... Full text Cite

Controlling error orientation to improve quantum algorithm success rates

Journal Article Physical Review A · March 14, 2019 The success probability of a quantum algorithm constructed from noisy quantum gates cannot be accurately predicted from single-parameter metrics that compare noisy and ideal gates. We illustrate this concept by examining a system with coherent errors and c ... Full text Cite

Quantum technologies and the National Quantum Initiative

Journal Article Quantum Engineering · March 2019 Full text Cite

Stabilizer Slicing: Coherent Error Cancellations in Low-Density Parity-Check Stabilizer Codes.

Journal Article Physical review letters · December 2018 Featured Publication Coherent errors are a dominant noise process in many quantum computing architectures. Unlike stochastic errors, these errors can combine constructively and grow into highly detrimental overrotations. To combat this, we introduce a simple technique for supp ... Full text Open Access Cite

Quantum Error Correction Decoheres Noise.

Journal Article Physical review letters · November 2018 Typical studies of quantum error correction assume probabilistic Pauli noise, largely because it is relatively easy to analyze and simulate. Consequently, the effective logical noise due to physically realistic coherent errors is relatively unknown. Here, ... Full text Cite

Spectroscopy of Molecular Ions in Coulomb Crystals.

Journal Article The journal of physical chemistry letters · October 2018 Featured Publication In this Perspective, we examine the use of laser-cooled atomic ions and sympathetically cooled molecular ions in Coulomb crystals for molecular spectroscopy. Coulomb crystals are well-isolated environments that provide localization and long storage times f ... Full text Cite

Entangling an arbitrary pair of qubits in a long ion crystal

Journal Article Physical Review A · September 18, 2018 It is well established that the collective motion of ion crystals can be used as a quantum bus for multiqubit entanglement. However, as the number of ions increases, it becomes difficult to directly entangle ions far apart and resolve all motional modes of ... Full text Cite

Comparing Zeeman qubits to hyperfine qubits in the context of the surface code: 174Yb+ and 171Yb+

Journal Article Phys. Rev. A · May 2, 2018 Featured Publication Many systems used for quantum computing possess additional states beyond those defining the qubit. Leakage out of the qubit subspace must be considered when designing quantum error correction codes. Here we consider trapped ion qubits manipulated by Raman ... Full text Link to item Cite

Direct measurement of Bacon-Shor code stabilizers

Journal Article · April 3, 2018 A Bacon-Shor code is a subsystem quantum error-correcting code on an $L \times L$ lattice where the $2(L-1)$ weight-$2L$ stabilizers are usually inferred from the measurements of $(L-1)^2$ weight-2 gauge operators. Here we show that the stabilizers can be ... Link to item Cite

Simulating the performance of a distance-3 surface code in a linear ion trap

Journal Article New Journal of Physics · April 1, 2018 Featured Publication We explore the feasibility of implementing a small surface code with 9 data qubits and 8 ancilla qubits, commonly referred to as surface-17, using a linear chain of 171Yb+ ions. Two-qubit gates can be performed between any two ions in the chain with gate t ... Full text Cite

Rovibronic Spectroscopy of Sympathetically Cooled 40CaH+

Journal Article The Journal of Physical Chemistry A · March 9, 2018 Featured Publication We measure the rovibronic transitions X 1Σ+, v″ = 0, J″ → A 1Σ+, v' = 0-3, J' of CaH+ and obtain rotational constants for the A 1Σ+ state. The spectrum is obtained using two-photon photodissociation of CaH+ cotrapped with Doppler cooled Ca+. The excitation ... Full text Cite

Robust 2-Qubit Gates in a Linear Ion Crystal Using a Frequency-Modulated Driving Force.

Journal Article Physical review letters · January 2018 Featured Publication In an ion trap quantum computer, collective motional modes are used to entangle two or more qubits in order to execute multiqubit logical gates. Any residual entanglement between the internal and motional states of the ions results in loss of fidelity, esp ... Full text Open Access Cite

Reassigning the CaH+ 11Σ → 21Σ vibronic transition with CaD.

Journal Article The Journal of chemical physics · December 2017 Featured Publication We observe vibronic transitions in CaD+ between the 11Σ and 21Σ electronic states by resonance enhanced multiphoton photodissociation spectroscopy in a Coulomb crystal. The vibronic transitions are compared with previous me ... Full text Cite

Optimized surface code communication in superconducting quantum computers

Conference Proceedings of the Annual International Symposium on Microarchitecture, MICRO · October 14, 2017 Quantum computing (QC) is at the cusp of a revolution. Machines with 100 quantum bits (qubits) are anticipated to be operational by 2020 [30, 73], and several-hundred-qubit machines are around the corner. Machines of this scale have the capacity to demonst ... Full text Cite

Fault-tolerant quantum error detection.

Journal Article Science advances · October 2017 Featured Publication Quantum computers will eventually reach a size at which quantum error correction becomes imperative. Quantum information can be protected from qubit imperfections and flawed control operations by encoding a single logical qubit in multiple physical qubits. ... Full text Cite

Fault tolerance with bare ancillary qubits for a [[7,1,3]] code

Journal Article Physical Review A · September 28, 2017 Featured Publication We present a [[7,1,3]] quantum error-correcting code that is able to achieve fault-tolerant syndrome measurement using one ancillary qubit per stabilizer for an error model of independent single-qubit Pauli errors. All single-qubit Pauli errors on the anci ... Full text Cite

Vibronic Spectroscopy of Sympathetically Cooled CaH.

Journal Article Chemphyschem : a European journal of chemical physics and physical chemistry · November 2016 Featured Publication We report the measurement of the 11 Σ→21 Σ transition of CaH+ by resonance-enhanced photodissociation of CaH+ that is co-trapped with laser-cooled Ca+ . We observe four resonances that we assign to tra ... Full text Cite

Errors and pseudothresholds for incoherent and coherent noise

Journal Article Physical Review A · October 24, 2016 We compare the effect of single qubit incoherent and coherent errors on the logical error rate of the Steane [[7,1,3]] quantum error correction code by performing an exact full-density-matrix simulation of an error correction step. We find that the effecti ... Full text Cite

Analytical error analysis of Clifford gates by the fault-path tracer method

Journal Article Quantum Information Processing · August 1, 2016 We estimate the success probability of quantum protocols composed of Clifford operations in the presence of Pauli errors. Our method is derived from the fault-point formalism previously used to determine the success rate of low-distance error correction co ... Full text Cite

Transport implementation of the Bernstein-Vazirani algorithm with ion qubits

Journal Article New Journal of Physics · August 1, 2016 Using trapped ion quantum bits in a scalable microfabricated surface trap, we perform the Bernstein-Vazirani algorithm. Our architecture takes advantage of the ion transport capabilities of such a trap. The algorithm is demonstrated using two- and three-io ... Full text Cite

Co-designing a scalable quantum computer with trapped atomic ions

Journal Article npj Quantum Information · January 1, 2016 Featured Publication The first generation of quantum computers are on the horizon, fabricated from quantum hardware platforms that may soon be able to tackle certain tasks that cannot be performed or modelled with conventional computers. These quantum devices will not likely b ... Full text Cite

Trapping and Sympathetic Cooling of Boron Ions

Journal Article · 2016 We demonstrate the trapping and sympathetic cooling of B$^{+}$ ions in a Coulomb crystal of laser-cooled Ca$^{+}$, We non-destructively confirm the presence of the both B$^+$ isotopes by resonant excitation of the secular motion. The B$^{+}$ ions are loade ... Link to item Cite

Error compensation of single-qubit gates in a surface-electrode ion trap using composite pulses

Journal Article · December 16, 2015 © 2015 American Physical Society.The fidelity of laser-driven quantum logic operations on trapped ion qubits tend to be lower than microwave-driven logic operations due to the difficulty of stabilizing the driving fields at the ion location. Through stabil ... Full text Open Access Cite

Modulating carrier and sideband coupling strengths in a standing-wave gate beam

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · December 10, 2015 We control the relative coupling strength of carrier and first-order motional sideband interactions of a trapped ion by placing it in a resonant optical standing wave. Our configuration uses the surface of a microfabricated chip trap as a mirror, avoiding ... Full text Cite

Magic state distillation and gate compilation in quantum algorithms for quantum chemistry

Journal Article International Journal of Quantum Chemistry · October 1, 2015 Quantum algorithms for quantum chemistry map the dynamics of electrons in a molecule to the dynamics of a coupled spin system. To reach chemical accuracy for interesting molecules, a large number of quantum gates must be applied which implies the need for ... Full text Cite

Observation of vibrational overtones by single-molecule resonant photodissociation.

Journal Article Nature communications · July 2015 Molecular ions can be held in a chain of laser-cooled atomic ions by sympathetic cooling. This system is ideal for performing high-precision molecular spectroscopy with applications in astrochemistry and fundamental physics. Here we show that this same sys ... Full text Cite

Compiler management of communication and parallelism for quantum computation

Conference International Conference on Architectural Support for Programming Languages and Operating Systems - ASPLOS · March 14, 2015 Quantum computing (QC) offers huge promise to accelerate a range of computationally intensive benchmarks. Quantum computing is limited, however, by the challenges of decoherence: i.e., a quantum state can only be maintained for short windows of time before ... Full text Cite

Sympathetic cooling of molecular ion motion to the ground state

Journal Article New Journal of Physics · March 12, 2015 We demonstrate sympathetic sideband cooling of a 40CaH+ molecular ion co-trapped with a 40Ca+ atomic ion in a linear Paul trap. Both axial modes of the two-ion chain are simultaneously cooled to near the ground state of motion. The center of mass mode is c ... Full text Cite

Comparison of a quantum error-correction threshold for exact and approximate errors

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · February 27, 2015 Classical simulations of noisy stabilizer circuits are often used to estimate the threshold of a quantum error-correcting code. Physical noise sources are efficiently approximated by random insertions of Pauli operators. For a single qubit, more accurate a ... Full text Cite

Laser-cooled atomic ions as probes of molecular ions

Conference AIP Conference Proceedings · January 1, 2015 Trapped laser-cooled atomic ions are a new tool for understanding cold molecular ions. The atomic ions not only sympathetically cool the molecular ions to millikelvin temperatures, but the bright atomic ion fluorescence can also serve as a detector of both ... Full text Cite

Transformed composite sequences for improved qubit addressing

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · October 2, 2014 Selective laser addressing of a single atom or atomic ion qubit can be improved using narrow-band composite pulse sequences. We describe a Lie-algebraic technique to generalize known narrow-band sequences and introduce sequences related by dilation and rot ... Full text Cite

Robustness of composite pulses to time-dependent control noise

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · July 14, 2014 We study the performance of composite pulses in the presence of time-varying control noise on a single qubit. These protocols, originally devised only to correct for static, systematic errors, are shown to be robust to time-dependent non-Markovian noise in ... Full text Cite

Heating rates and ion-motion control in a y -junction surface-electrode trap

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · June 6, 2014 We measure ion heating following transport throughout a Y-junction surface-electrode ion trap. By carefully selecting the trap voltage update rate during adiabatic transport along a trap arm, we observe minimal heating relative to the anomalous heating bac ... Full text Cite

Large-scale modular quantum-computer architecture with atomic memory and photonic interconnects

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · February 13, 2014 The practical construction of scalable quantum-computer hardware capable of executing nontrivial quantum algorithms will require the juxtaposition of different types of quantum systems. We analyze a modular ion trap quantum-computer architecture with a hie ... Full text Cite

Physics Probing the electron.

Journal Article Science (New York, N.Y.) · January 2014 Full text Cite

Comparison of ancilla preparation and measurement procedures for the Steane [[7,1,3]] code on a model ion-trap quantum computer

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · October 30, 2013 We schedule the Steane [[7,1,3]] error correction on a model ion-trap architecture with ballistic transport. We compare the level-1 error rates for syndrome extraction using the Shor method of ancilla prepared in verified cat states to the DiVincenzo-Alife ... Full text Cite

Identifying single molecular ions by resolved sideband measurements.

Journal Article The journal of physical chemistry. A · October 2013 The masses of single molecular ions are nondestructively measured by cotrapping the ion of interest with a laser-cooled atomic ion, (40)Ca(+). Measurement of the resolved sidebands of a dipole forbidden transition on the atomic ion reveals the normal-mode ... Full text Cite

Quantum rotations: A case study in static and dynamic machine-code generation for quantum computers

Conference Proceedings - International Symposium on Computer Architecture · August 12, 2013 Work in quantum computer architecture has focused on communication, layout and fault tolerance, largely driven by Shor's factorization algorithm. For the first time, we study a larger range of benchmarks and find that another critical issue is the generati ... Full text Cite

Spatially uniform single-qubit gate operations with near-field microwaves and composite pulse compensation

Journal Article New Journal of Physics · August 1, 2013 We present a microfabricated surface-electrode ion trap with a pair of integrated waveguides that generate a standing microwave field resonant with the 171Yb+ hyperfine qubit. The waveguides are engineered to position the wave antinode near the center of t ... Full text Cite

Modular cryostat for ion trapping with surface-electrode ion traps.

Journal Article The Review of scientific instruments · April 2013 We present a simple cryostat purpose built for use with surface-electrode ion traps, designed around an affordable, large cooling power commercial pulse tube refrigerator. A modular vacuum enclosure with a single vacuum space facilitates interior access an ... Full text Cite

Approximation of realistic errors by Clifford channels and Pauli measurements

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · March 22, 2013 The Gottesman-Knill theorem allows for the efficient simulation of stabilizer-based quantum error-correction circuits. Errors in these circuits are commonly modeled as depolarizing channels by using Monte Carlo methods to insert Pauli gates randomly throug ... Full text Cite

Techniques for microwave near-field quantum control of trapped ions

Journal Article Physical Review A · January 31, 2013 Full text Cite

Topological subsystem codes from graphs and hypergraphs

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · October 31, 2012 Topological subsystem codes were proposed by Bombin based on 3-face-colorable cubic graphs. Suchara, Bravyi, and Terhal generalized this construction and proposed a method to construct topological subsystem codes using 3-valent hypergraphs that satisfy cer ... Full text Cite

Demonstration of integrated microscale optics in surface-electrode ion traps

Journal Article New Journal of Physics · October 1, 2011 In ion trap quantum information processing, efficient fluorescence collection is critical for fast, high-fidelity qubit detection and ion-photon entanglement. The expected size of future many-ion processors requires scalable light collection systems. We re ... Full text Cite

Single-qubit-gate error belowin a trapped ion

Journal Article Physical Review A · September 14, 2011 Full text Cite

Microwave quantum logic gates for trapped ions.

Journal Article Nature · August 2011 Control over physical systems at the quantum level is important in fields as diverse as metrology, information processing, simulation and chemistry. For trapped atomic ions, the quantized motional and internal degrees of freedom can be coherently manipulat ... Full text Cite

Challenges of laser-cooling molecular ions

Journal Article New Journal of Physics · June 1, 2011 The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides an opportunity for multi-step cooling ... Full text Cite

Coupled quantized mechanical oscillators.

Journal Article Nature · March 2011 The harmonic oscillator is one of the simplest physical systems but also one of the most fundamental. It is ubiquitous in nature, often serving as an approximation for a more complicated system or as a building block in larger models. Realizations of harmo ... Full text Cite

Sympathetic heating spectroscopy of atomic and molecular ions

Conference ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY · 2011 Cite

Sympathetic heating spectroscopy: Probing molecular ions with laser-cooled atomic ions

Conference Optics InfoBase Conference Papers · December 1, 2010 Sympathetic heating spectroscopy measures atomic and molecular ion spectra by observing the heating of a laser-cooled control ion. Limits of the method are tested using two isotopes of calcium. Applications for molecular ions are discussed. © 2010 OSA /FiO ... Cite

Analytical solution of thermal magnetization on memory stabilizer structures

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · October 6, 2010 We return to the question of how the choice of stabilizer generators affects the preservation of information on structures whose degenerate ground state encodes a classical redundancy code. Controlled-not gates are used to transform the stabilizer Hamilton ... Full text Cite

Making classical ground-state spin computing fault-tolerant.

Journal Article Physical review. E, Statistical, nonlinear, and soft matter physics · September 2010 We examine a model of classical deterministic computing in which the ground state of the classical system is a spatial history of the computation. This model is relevant to quantum dot cellular automata as well as to recent universal adiabatic quantum comp ... Full text Cite

Detection of single-ion spectra by Coulomb-crystal heating

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · April 29, 2010 The coupled motion of ions in a radiofrequency trap has been used to connect the frequency-dependent laser-induced heating of a sympathetically cooled spectroscopy ion with changes in the fluorescence of a laser-cooled control ion. This technique, sympathe ... Full text Cite

Quantum computing: chemistry from photons.

Journal Article Nature chemistry · February 2010 Full text Cite

Multi-qubit compensation sequences

Journal Article New Journal of Physics · January 19, 2010 The Hamiltonian control of n qubits requires precision control of both the strength and timing of interactions. Compensation pulses relax the precision requirements by reducing unknown but systematic errors. Using composite pulse techniques designed for si ... Full text Cite

Laser-cooled atomic ions as probes of molecular ions for applications in astrochemistry

Conference ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY · 2010 Cite

Design and characterization of a planar trap

Journal Article Journal of Physics B: Atomic, Molecular and Optical Physics · November 9, 2009 We demonstrate laser cooling of 40Ca+ ions in a linear-type planar trap where all electrodes are located in a plane. We numerically calculate the potential of a 500 νm scale trap and then characterize the trap by measuring the secular frequencies. Linear c ... Full text Cite

Monte Carlo analysis of critical phenomenon of the Ising model on memory stabilizer structures

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · October 19, 2009 We calculate the critical temperature of the Ising model on a set of graphs representing a concatenated three-bit error-correction code. The graphs are derived from the stabilizer formalism used in quantum error correction. The stabilizer for a subspace is ... Full text Cite

A two-dimensional lattice ion trap for quantum simulation

Journal Article Journal of Applied Physics · July 9, 2009 Quantum simulations of spin systems could enable the solution of problems that otherwise require infeasible classical resources. Such a simulation may be implemented using a well-controlled system of effective spins, such as a two-dimensional lattice of lo ... Full text Cite

Resource requirements for fault-tolerant quantum simulation: The ground state of the transverse Ising model

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · June 15, 2009 We estimate the resource requirements, the total number of physical qubits and computational time, required to compute the ground-state energy of a one-dimensional quantum transverse Ising model (TIM) of N spin-1/2 particles, as a function of the system si ... Full text Cite

Suppression of heating rates in cryogenic surface-electrode ion traps.

Journal Article Physical review letters · January 2008 Dense arrays of trapped ions provide one way of scaling up ion trap quantum information processing. However, miniaturization of ion traps is currently limited by sharply increasing motional state decoherence at sub-100 mum ion-electrode distances. We chara ... Full text Cite

Laser ablation loading of a surface-electrode ion trap

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · November 8, 2007 We demonstrate loading of Sr+88 ions by laser ablation into a mm-scale surface-electrode ion trap. The laser used for ablation is a pulsed, frequency-tripled Nd:YAG with pulse energies of 1-10 mJ and durations of 4 ns. An additional laser is not required t ... Full text Cite

Passive cooling of a micromechanical oscillator with a resonant electric circuit

Journal Article Physical Review Letters · September 26, 2007 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 cool ... Full text Cite

Energy protection arguments fail in the interaction picture

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · August 23, 2007 Spin Hamiltonians with degenerate ground states are one potential system for the storage of quantum information at low temperatures. Trapped ions can be used to simulate the dynamics of these Hamiltonians, but the coherence-preserving properties will be lo ... Full text Cite

Compact, filtered diode laser system for precision spectroscopy.

Journal Article Optics letters · March 2007 Stable, narrow-linewidth optical sources are necessary in modern atomic physics. An appealing approach to achieving approximately 10 kHz frequency stability is optical feedback. We have designed a compact external cavity diode laser with optical feedback t ... Full text Cite

Loading and characterization of a printed-circuit-board atomic ion trap

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · January 30, 2007 We demonstrate loading of Sr+88 ions into a 0.5-mm -scale printed circuit board surface-electrode ion trap. We then characterize the trap by measuring the secular frequencies and comparing them to a three-dimensional simulation of the trap, and by measurin ... Full text Cite

Limitations of quantum simulation examined by simulating a pairing Hamiltonian using nuclear magnetic resonance.

Journal Article Physical review letters · August 2006 Quantum simulation uses a well-known quantum system to predict the behavior of another quantum system. Certain limitations in this technique arise, however, when applied to specific problems, as we demonstrate with a theoretical and experimental study of a ... Full text Cite

Experimental investigation of planar ion traps

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · March 10, 2006 Chiaverini [Quantum Inf. Comput. 5, 419 (2005)] recently suggested a linear Paul trap geometry for ion-trap quantum computation that places all of the electrodes in a plane. Such planar ion traps are compatible with modern semiconductor fabrication techniq ... Full text Cite

Bose-Einstein condensation in a mm-scale Ioffe-Pritchard trap

Journal Article Applied Physics B: Lasers and Optics · March 1, 2006 We have constructed a mm-scale Ioffe-Pritchard trap capable of providing axial field curvature of 7800 G/cm2 with only 10.5 A of driving current. Our novel fabrication method involving electromagnetic coils formed of anodized aluminum strips is compatible ... Full text Cite

Erratum: Arbitrarily accurate composite pulse sequences (Physics Review A (2004) 70 (052318))

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · September 1, 2005 Full text Cite

Full protection of superconducting qubit systems from coupling errors

Journal Article Physical Review B - Condensed Matter and Materials Physics · August 1, 2005 Solid state qubits realized in superconducting circuits are potentially scalable. However, strong decoherence may be transferred to the qubits by various elements of the circuits that couple individual qubits, particularly when coupling is implemented over ... Full text Cite

Bounds on the entanglement attainable from unitary transformed thermal states in liquid-state nuclear magnetic resonance

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · March 1, 2005 The role of mixed-state entanglement in liquid-state nuclear magnetic resonance (NMR) quantum computation is not yet well understood. In particular, despite the success of quantum-information processing with NMR, recent work has shown that quantum states u ... Full text Cite

Arbitrarily accurate composite pulse sequences

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · November 1, 2004 A systematic technique for creating composite pulse sequences to correct errors to O (εn) for arbitrary n was discussed. The technique presented was found to be general and could be used to correct a wide range of systematic errors. These pulses also allow ... Full text Cite

Transmission spectrum of an optical cavity containing N atoms

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · January 1, 2004 The strong-coupling cavity quantum electrodynamics (CQED) effects were used for counting the number of traped atoms inside a high-finesse optical microcavity. The Tavis-Cummings model was used to predict the transmission spectrum of a cavity containing N i ... Full text Cite

Scalable ion trap quantum computation in decoherence-free subspaces with pairwise interactions only

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · January 1, 2003 We show that universal ion trap computation can be performed on decoherence-free subspaces (DFS’s) using only two-qubit operations. One logical qubit is minimally encoded into three physical qubits. The encoded qubit is in a DFS under collective decoherenc ... Full text Cite

Effects of a random noisy oracle on search algorithm complexity

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · January 1, 2003 Grover’s algorithm provides a quadratic speed-up over classical algorithms for unstructured database or library searches. This paper examines the robustness of Grover’s search algorithm to a random phase error in the oracle and analyzes the complexity of t ... Full text Cite

Deterministic optical Fock-state generation

Journal Article Physical Review A - Atomic, Molecular, and Optical Physics · January 1, 2003 We present a scheme for the deterministic generation of N-photon Fock states from N three-level atoms in a high-finesse optical cavity. The method applies an external laser pulse that generates an N-photon output state while adiabatically keeping the atom- ... Full text Cite

Quantum computing with quantum dots on quantum linear supports

Journal Article Physical Review A. Atomic, Molecular, and Optical Physics · January 1, 2002 A scheme for quantum computation was proposed using chemically assembled semiconductor nanocrystals attached to a linear support. The linear support was either a nanoscale rod or a molecular string and its phonon modes were used as a quantum-information bu ... Cite

Coherence-preserving quantum bits.

Journal Article Physical review letters · December 2001 Real quantum systems couple to their environment and lose their intrinsic quantum nature through the process known as decoherence. Here we present a method for minimizing decoherence by making it energetically unfavorable. We present a Hamiltonian made up ... Full text Cite

ACTIVE-SITE STUDIES ON PARATHION HYDROLASE

Conference ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY · 1994 Cite

Concentrations of copper, zinc and lead in the Sydney rock oyster, Saccostrea commercialis (Iredale and Roughley) from the Georges River, New South Wales.

Journal Article The Science of the total environment · September 1992 Copper, zinc and lead were analysed from samples of non-commercially grown Sydney rock oysters collected from the Georges River estuary in spring 1987. The results, when compared with previous data from 1975, indicated a marked increase in the concentratio ... Full text Cite

Blowfly succession — a simple trap

Journal Article Journal of Biological Education · June 1991 Full text Cite

LAMINATED METAL COMPOSITES OF ULTRAHIGH CARBON-STEEL BRASS AND AL/AL-SIC - PROCESSING AND PROPERTIES

Conference DEVELOPMENTS IN CERAMIC AND METAL-MATRIX COMPOSITES · 1991 Cite