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Thermal and residual excited-state population in a 3D transmon qubit

June 19, 2015
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Journal Article
Author:
X. Y. Jin
…
Published in:
Phys. Rev. Lett., Vol. 114, No. 24, 19 June 2015, 240501.
Topic:
computing
R&D area:
R&D group:

Summary

Remarkable advancements in coherence and control fidelity have been achieved in recent years with cryogenic solid-state qubits. Nonetheless, thermalizing such devices to their milliKelvin environments has remained a long-standing fundamental and technical challenge. In this context, we present a systematic study of the first-excited-state population in a 3D transmon superconducting qubit mounted in a dilution refrigerator with a variable temperature. Using a modified version of the protocol developed by Geerlings et al., we observe the excited-state population to be consistent with a Maxwell-Boltzmann distribution, i.e., a qubit in thermal equilibrium with the refrigerator, over the temperature range 35-150 mK. Below 35 mK, the excited-state population saturates at approximately 0.1%. We verified this result using a flux qubit with ten times stronger coupling to its readout resonator. We conclude that these qubits have effective temperature Teff ơ 35 mK. Assuming Teff is due solely to hot quasiparticles, the inferred qubit lifetime is 108 microns and in plausible agreement with the measured 80 microns.
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Summary

Remarkable advancements in coherence and control fidelity have been achieved in recent years with cryogenic solid-state qubits. Nonetheless, thermalizing such devices to their milliKelvin environments has remained a long-standing fundamental and technical challenge. In this context, we present a systematic study of the first-excited-state population in a 3D transmon superconducting...

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Thermal and residual excited-state population in a 3D transmon qubit

Broadband magnetometry and temperature sensing with a light-trapping diamond waveguide

April 6, 2015
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Journal Article
Author:
Hannah Clevenson
…
Published in:
Nature Phys. Lett., Vol. 11, May 2015, pp. 393-7.
Topic:
sensing
R&D area:
R&D group:

Summary

Solid-state quantum sensors are attracting wide interest because of their sensitivity at room temperature. In particular, the spin properties of individual nitrogen-vacancy (NV) colour centres in diamond make them outstanding nanoscale sensors of magnetic fields, electric fields and temperature under ambient conditions. Recent work on NV ensemble-based magnetometers, inertial sensors, and clocks has employed unentangled colour centres to realize significant improvements in sensitivity. However, to achieve this potential sensitivity enhancement in practice, new techniques are required to excite efficiently and to collect the optical signal from large NV ensembles. Here, we introduce a light-trapping diamond waveguide geometry with an excitation efficiency and signal collection that enables in excess of 5% conversion efficiency of pump photons into optically detected magnetic resonance (ODMR) fluorescence--an improvement over previous single-pass geometries of more than three orders of magnitude. This marked enhancement of the ODMR signal enables precision broadband measurements of magnetic field and temperature in the low-frequency range, otherwise inaccessible by dynamical decoupling techniques.
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Summary

Solid-state quantum sensors are attracting wide interest because of their sensitivity at room temperature. In particular, the spin properties of individual nitrogen-vacancy (NV) colour centres in diamond make them outstanding nanoscale sensors of magnetic fields, electric fields and temperature under ambient conditions. Recent work on NV ensemble-based magnetometers, inertial sensors...

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Broadband magnetometry and temperature sensing with a light-trapping diamond waveguide

Measurement of ion motional heating rates over a range of trap frequencies and temperatures

April 1, 2015
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Journal Article
Author:
Colin D. Bruzewicz
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Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 91, No. 4, April 2015, 041402.
Topic:
quantum
R&D area:
R&D group:

Summary

We present measurements of the motional heating rate of a trapped ion at different trap frequencies and temperatures between ~0.6 and 1.5 MHz and ~4 and 295 K. Additionally, we examine the possible effect of adsorbed surface contaminants with boiling points below ~105 degrees C by measuring the ion heating rate before and after locally baking our ion trap chip under ultrahigh vacuum conditions. We compare the heating rates presented here to those calculated from available electric-field noise models. We can tightly constrain a subset of these models based on their expected frequency and temperature scaling interdependence. Discrepancies between the measured results and predicted values point to the need for refinement of theoretical noise models in order to more fully understand the mechanisms behind motional trapped-ion heating.
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Summary

We present measurements of the motional heating rate of a trapped ion at different trap frequencies and temperatures between ~0.6 and 1.5 MHz and ~4 and 295 K. Additionally, we examine the possible effect of adsorbed surface contaminants with boiling points below ~105 degrees C by measuring the ion heating...

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Measurement of ion motional heating rates over a range of trap frequencies and temperatures

Increasing the coherence time in a magnetically-sensitive stimulated Raman transition in 85Rb

October 14, 2014
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Conference Paper
Author:
Sara A. DeSavage
…
Published in:
FIO 2014: Frontiers in Optics, 14 October 2014.
Topic:
quantum
R&D area:
R&D group:

Summary

We experimentally study the Ramsey, spin echo, and CPMG pulse sequences of a magnetically sensitive transition of a cold 85Rb gas. We can increase the coherence time by up to a factor of 10 by using CPMG pulse sequences as compared to Ramsey or spin echo.
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Summary

We experimentally study the Ramsey, spin echo, and CPMG pulse sequences of a magnetically sensitive transition of a cold 85Rb gas. We can increase the coherence time by up to a factor of 10 by using CPMG pulse sequences as compared to Ramsey or spin echo.

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Increasing the coherence time in a magnetically-sensitive stimulated Raman transition in 85Rb

Insensitivity of the rate of ion motional heating to trap-electrode material over a large temperature range

January 16, 2014
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Journal Article
Author:
John Chiaverini
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Published in:
Phys. Rev. A, At. Mol. Opt. Phys., Vol. 89, No. 1, 2014, 012318.
Topic:
advanced materials
R&D area:
R&D group:

Summary

We present measurements of trapped-ion motional-state heating rates in niobium and gold surface-electrode ion traps over a range of trap-electrode temperatures from approximately 4 K to room temperature (295 K) in a single apparatus. Using the sideband-ratio technique after resolved-sideband cooling of single ions to the motional ground state, we find low-temperature heating rates more than two orders of magnitude below the room-temperature values and approximately equal to the lowest measured heating rates in similarly sized cryogenic traps. We find similar behavior in the two very different electrode materials, suggesting that the anomalous heating process is dominated by non-material-specific surface contaminants. Through precise control of the temperature of cryopumping surfaces, we also identify conditions under which elastic collisions with the background gas can lead to an apparent steady heating rate, despite rare collisions.
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Summary

We present measurements of trapped-ion motional-state heating rates in niobium and gold surface-electrode ion traps over a range of trap-electrode temperatures from approximately 4 K to room temperature (295 K) in a single apparatus. Using the sideband-ratio technique after resolved-sideband cooling of single ions to the motional ground state, we...

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Insensitivity of the rate of ion motional heating to trap-electrode material over a large temperature range

A frequency selective atom interferometer magnetometer

January 13, 2014
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Journal Article
Author:
Danielle A. Braje
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Published in:
J. Mod. Opt., Vol. 61, No. 1, 2014, pp. 61-71.
Topic:
optics
R&D area:
R&D group:

Summary

In this article, we discuss the magnetic-field frequency selectivity of a time-domain interferometer based on the number and timing of intermediate pi pulses. We theoretically show that by adjusting the number of pi pulses and the pi-pulse timing, we can control the frequency selectivity of the interferometer to time varying and DC magnetic fields. We present experimental data demonstrating increased coherence time due to bandwidth filtering with the inclusion of a pi pulse between the initial and final pi/2 pulses, which mitigates sensitivity to low frequency magnetic fields.
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Summary

In this article, we discuss the magnetic-field frequency selectivity of a time-domain interferometer based on the number and timing of intermediate pi pulses. We theoretically show that by adjusting the number of pi pulses and the pi-pulse timing, we can control the frequency selectivity of the interferometer to time varying...

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A frequency selective atom interferometer magnetometer

Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators

December 6, 2013
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Journal Article
Author:
Andrew J. Kerman
Published in:
New J. Phys., Vol. 15, 2013, 123011.
Topic:
quantum
R&D area:
R&D group:

Summary

Electrical resonators are widely used in quantum information processing, by engineering an electromagnetic interaction with qubits based on real or virtual exchange of microwave photons. This interaction relies on strong coupling between the qubits' transition dipole moments and the vacuum fluctuations of the resonator in the same manner as cavity quantum electrodynamics (QED), and has consequently come to be called 'circuit QED' (cQED). Great strides in the control of quantum information have already been made experimentally using this idea. However, the central role played by photon exchange induced by quantum fluctuations in cQED does result in some characteristic limitations. In this paper, we discuss an alternative method for coupling qubits electromagnetically via a resonator, in which no photons are exchanged, and where the resonator need not have strong quantum fluctuations. Instead, the interaction can be viewed in terms of classical, effective 'forces' exerted by the qubits on the resonator, and the resulting resonator dynamics used to produce qubit entanglement are purely classical nature. We show how this type of interaction is similar to that encountered in the manipulation of atomic ion qubits, and we exploit this analogy to construct two-qubit entangling operations that are largely insensitive to thermal or other noise in the resonator, and to its quality factor. These operations are also extensisble to larger numbers of qubits, allowing interactions to be selectively generated among any desired subset of those coupled to a single resonator. Our proposal is potentially applicable to a variety of physical qubit modalities, including superconducting and semiconducting solid-state qubits, trapped molecular ions, and possibly even electron spins in solids.
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Summary

Electrical resonators are widely used in quantum information processing, by engineering an electromagnetic interaction with qubits based on real or virtual exchange of microwave photons. This interaction relies on strong coupling between the qubits' transition dipole moments and the vacuum fluctuations of the resonator in the same manner as cavity...

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Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators

Flux-charge duality and topological quantum phase fluctuations in quasi-one-dimensional superconductors

October 18, 2013
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Journal Article
Author:
Andrew J. Kerman
Published in:
New J. Phys., Vol. 15, 2013, 105017.
Topic:
quantum
R&D area:
R&D group:

Summary

It has long been thought that macroscopic phase coherence breaks down in effectively lower-dimensional superconducting systems even at zero temperature due to enhanced topological quantum phase fluctuations. In quasi-one-dimensional wires, these fluctuations are described in terms of 'quantum phase-slip' (QPS): tunneling of the superconducting order parameter for the wire between states differing by plus or minus 2 pi in their relative phase between the wire's ends. Over the last several decades, many deviations from conventional bulk superconducting behavior have been observed in ultra-narrow superconducting nanowires, some of which have been identified with QPS. While at least some of the observations are consistent with existing theories for QPS, other observations in many cases point to contradictory conclusions or cannot be explained by these theories. Hence, our understanding of the nature of QPS, and its relationship to the various observations, has remained incomplete. In this paper we present a new model for QPS which takes as its starting point an idea originally postulated by Mooij and Nazarov (2006 Nature Phys. 2 169): that flux-charge duality, a classical symmertry of Maxwell's equations, can be used to relate QPS to the well-known Josephson tunneling of Cooper pairs. Our model provides an alternative, and qualitatively different, conceptual basis for QPS and the phenomena which arise from it in experiments, and it appears to permit for the first time a unified understanding of observations across several different types of experiments and materials systems.
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Summary

It has long been thought that macroscopic phase coherence breaks down in effectively lower-dimensional superconducting systems even at zero temperature due to enhanced topological quantum phase fluctuations. In quasi-one-dimensional wires, these fluctuations are described in terms of 'quantum phase-slip' (QPS): tunneling of the superconducting order parameter for the wire between...

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Flux-charge duality and topological quantum phase fluctuations in quasi-one-dimensional superconductors

Materials in superconducting quantum bits

October 1, 2013
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Journal Article
Author:
William D. Oliver
…
Published in:
MRS Bulletin, Vol 38, October 2013, pp. 816-825.
Topic:
advanced materials
R&D area:
R&D group:

Summary

Superconducting qubits are electronic circuits comprising lithographically defined Josephson tunnel junctions, inductors, capacitors, and interconnects. When cooled to dillution refrigerator temperatures, these circuits behave as quantum mechanical "artificial atoms," exhibiting quantized states of electronic charge, magnetic flux, or junction phase depending on the design parameters of the constituent circuit elements. Their potential for lithographic scalability, compatibility with microwave control, and operability at nanosecond time scales place superconducting qubits among the leading modalities being considered for quantum information science and technology applications. Over the past decade, the quantum coherence of superconducting qubits has increased more than five orders of magnitude, due primarily to improvements in their design, fabrication, and, importantly, their constituent materials and interfaces. In this article, we review superconducting qubits, articulate the important role of materials research in their development, and provide a prospectus for the future as these devices transition from scientific curiosity to the threshold of technical reality.
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Summary

Superconducting qubits are electronic circuits comprising lithographically defined Josephson tunnel junctions, inductors, capacitors, and interconnects. When cooled to dillution refrigerator temperatures, these circuits behave as quantum mechanical "artificial atoms," exhibiting quantized states of electronic charge, magnetic flux, or junction phase depending on the design parameters of the constituent circuit elements...

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Materials in superconducting quantum bits

A tunable AC atom interferometer magnetometer

June 17, 2013
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Conference Paper
Author:
Danielle A. Braje
…
Published in:
QIM 2013, Quantum Information and Measurement, 17-20 June 2013.
Topic:
optics
R&D area:
R&D group:

Summary

We demonstrate an atom interferometer designed to measure magnetic fields and field gradients. Here, we study various pulse sequences and show how they can be manipulated to filter unwanted frequencies and to enhance desired frequencies.
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Summary

We demonstrate an atom interferometer designed to measure magnetic fields and field gradients. Here, we study various pulse sequences and show how they can be manipulated to filter unwanted frequencies and to enhance desired frequencies.

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A tunable AC atom interferometer magnetometer
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