IARPA: Advances in Superconducting Qubits Materials and Fabrication Grant

Two Levels of proposals are sought, with particular interest in application to the
phase qubit:

Level I proposals will seek to accomplish all of the following Program Goals:
(1) fundamental understanding and insights into defects in superconducting
qubits that currently limit coherence time and readout contrast; (2) means to
characterize, measure and definitively discriminate between these separate
defects; and (3) advanced materials, constructions and fabrication methods to
eliminate these defects.

Level II proposals will seek to accomplish Level I goals as well as the
following additional Program Goal: (4) demonstrate substantially extended
coherence times in superconducting qubits fabricated from foregoing
developments.
With regard to developing fundamental understanding of superconducting
qubit defects, there are several research topics of interest; including but not
limited to:

– The origin of defects in “lossy” materials leading to two-level-systems that
couple to qubit state transitions; defects whose population for example is reflected
by the characteristic “splitting density” observed in readout spectroscopy of the
phase qubit.

– The origin of 1/f noise (charge, current and flux noise) and associated
electronic mechanisms affecting qubit performance as a function of temperature,
but with emphasis on the operating conditions of the qubit. (e.g. for the phase
qubit… 25 mK, low power, GHz …).

-The role of interface and surface quality attributes including:

-physical uniformity, smoothness and definition
-chemical composition, cleanliness or contamination (stoichiometry,
deleterious oxides, impurities…)
-morphology (crystallinity, crystal orientation, grain size …)
-stability of all of the above (e.g. a junction is considered unstable from
which oxygen diffuses into adjacent layers, resulting in an evolution of
stoichiometry and potentially crystallinity and thus electronic properties(e.g.
dielectric loss tangent))

– The effects of coherence length mismatch between dissimilar top and bottom
electrodes

– Novel measurement techniques for isolating decoherence mechanisms and
quantifying their relative contribution.

– Defects that may be intrinsic to specific device architectures such as junction
type (SIS, SNS, ScS (constriction or microbridge junctions) or SvS (vacuum
junctions)), junction geometry, qubit geometry and layout.

– The correlation between alternative materials metrics and qubit performance

– The role overall qubit size and junction bias current plays, in combination
with defects, in enhancing or reducing energy decay and phase coherence in
different forms of qubits. For example, ultra small flux and transmon qubits (with
ultra-small junctions) have demonstrated better coherence performance (T1 and
T2) than larger flux and current-biased phase qubits (with larger junctions).

– The role defects in junctions plays in contributing to energy loss when
incorporated into different configurations of resonant circuits from coplanar
waveguides to lumped-element resonators, challenging the notion of
“dissipationless” Josephson junctions.

– New concepts in decoherence mechanisms

Any combination of the above and or additional topics may be included in a
proposal. In general, for all topics pursued in developing fundamental
understanding of superconducting qubit defects, proposals should focus on:

a) developing a full understanding of the defect types, the mechanisms by
which they occur, the mechanisms by which they affect the qubit, and the
qubit performance characteristics they limit (coherence time, contrast, etc.),

b) the means for definitive characterization and measurement of those defects
in the presence of other defects, and subsequently

c) the most effective means for their elimination.

Note: proposals should also describe test platforms to be used in initial studies of
decoherence mechanisms, materials screening and process development. Test
platforms such as, but not limited to resonators and antennas should be proposed
in appropriate detail, including physically descriptive drawings or photographs
and electrical schematics. Details should be given on how the test platform will
measure the desired materials properties and how, if possible, the platform can be
used to equivalently reveal qubit performance metrics. The correlation between
selected materials metrics and qubit performance should be unambiguously
supported by a description of theoretical as well as experimental evidence.
With regard to advanced materials and fabrication methods, there are several
research topics of interest; including but not limited to:
– Tunnel junctions of high physical, chemical, morphological, etc… quality and
stability, as well as high critical current and critical current uniformity
– Ultra low-loss dielectrics for insulators and junctions and characterization of
detrimental effects of impurities and imperfections therein as a result of the
fabrication process
– Advanced electrode materials and or passivation layers to minimize 1/f noise
from interfaces, electrode surfaces and wiring
– Control of contamination from magnetic materials, such as iron
– High purity materials for sputtering targets
– Innovative qubit designs that may for example a) minimize or eliminate
materials contributing to decoherence (e.g. through vacuum insulators, etc…), or
b) circumvent deleterious mechanisms intrinsic to conventional geometries (e.g.
through alternative geometries and or vacuum or normal metal or constriction
barriers)
– Fabrication techniques providing superior materials and reproducibility
– Fabrication quality of electrodes, including the effects of rough edges
– Chamber(s) characterization (e.g., temperature, gases, other materials in the
chamber) for depositing films and oxidation for fabricating reproducible high
quality qubits
– New concepts in materials and fabrication techniques or qubit designs
Any combination of the above and or additional topics may be included in a given
proposal. In general, for all topics pursued in advanced materials and fabrication
methods, proposals should focus on developing materials advances, fabrication
techniques, and junction or qubit designs that will substantially eliminate
decoherence mechanisms and significantly improve qubit performance.

Two Levels of proposals are sought, with particular interest in application to the
phase qubit:

Level I proposals will seek to accomplish all of the following Program Goals:
(1) fundamental understanding and insights into defects in superconducting
qubits that currently limit coherence time and readout contrast; (2) means to
characterize, measure and definitively discriminate between these separate
defects; and (3) advanced materials, constructions and fabrication methods to
eliminate these defects.

Level II proposals will seek to accomplish Level I goals as well as the
following additional Program Goal: (4) demonstrate substantially extended
coherence times in superconducting qubits fabricated from foregoing
developments.
With regard to developing fundamental understanding of superconducting
qubit defects, there are several research topics of interest; including but not
limited to:

– The origin of defects in “lossy” materials leading to two-level-systems that
couple to qubit state transitions; defects whose population for example is reflected
by the characteristic “splitting density” observed in readout spectroscopy of the
phase qubit.

– The origin of 1/f noise (charge, current and flux noise) and associated
electronic mechanisms affecting qubit performance as a function of temperature,
but with emphasis on the operating conditions of the qubit. (e.g. for the phase
qubit… 25 mK, low power, GHz …).

-The role of interface and surface quality attributes including:

-physical uniformity, smoothness and definition
-chemical composition, cleanliness or contamination (stoichiometry,
deleterious oxides, impurities…)
-morphology (crystallinity, crystal orientation, grain size …)
-stability of all of the above (e.g. a junction is considered unstable from
which oxygen diffuses into adjacent layers, resulting in an evolution of
stoichiometry and potentially crystallinity and thus electronic properties(e.g.
dielectric loss tangent))

– The effects of coherence length mismatch between dissimilar top and bottom
electrodes

– Novel measurement techniques for isolating decoherence mechanisms and
quantifying their relative contribution.

– Defects that may be intrinsic to specific device architectures such as junction
type (SIS, SNS, ScS (constriction or microbridge junctions) or SvS (vacuum
junctions)), junction geometry, qubit geometry and layout.

– The correlation between alternative materials metrics and qubit performance

– The role overall qubit size and junction bias current plays, in combination
with defects, in enhancing or reducing energy decay and phase coherence in
different forms of qubits. For example, ultra small flux and transmon qubits (with
ultra-small junctions) have demonstrated better coherence performance (T1 and
T2) than larger flux and current-biased phase qubits (with larger junctions).

– The role defects in junctions plays in contributing to energy loss when
incorporated into different configurations of resonant circuits from coplanar
waveguides to lumped-element resonators, challenging the notion of
“dissipationless” Josephson junctions.

– New concepts in decoherence mechanisms

Any combination of the above and or additional topics may be included in a
proposal. In general, for all topics pursued in developing fundamental
understanding of superconducting qubit defects, proposals should focus on:

a) developing a full understanding of the defect types, the mechanisms by
which they occur, the mechanisms by which they affect the qubit, and the
qubit performance characteristics they limit (coherence time, contrast, etc.),

b) the means for definitive characterization and measurement of those defects
in the presence of other defects, and subsequently

c) the most effective means for their elimination.

Note: proposals should also describe test platforms to be used in initial studies of
decoherence mechanisms, materials screening and process development. Test
platforms such as, but not limited to resonators and antennas should be proposed
in appropriate detail, including physically descriptive drawings or photographs
and electrical schematics. Details should be given on how the test platform will
measure the desired materials properties and how, if possible, the platform can be
used to equivalently reveal qubit performance metrics. The correlation between
selected materials metrics and qubit performance should be unambiguously
supported by a description of theoretical as well as experimental evidence.
With regard to advanced materials and fabrication methods, there are several
research topics of interest; including but not limited to:
– Tunnel junctions of high physical, chemical, morphological, etc… quality and
stability, as well as high critical current and critical current uniformity
– Ultra low-loss dielectrics for insulators and junctions and characterization of
detrimental effects of impurities and imperfections therein as a result of the
fabrication process
– Advanced electrode materials and or passivation layers to minimize 1/f noise
from interfaces, electrode surfaces and wiring
– Control of contamination from magnetic materials, such as iron
– High purity materials for sputtering targets
– Innovative qubit designs that may for example a) minimize or eliminate
materials contributing to decoherence (e.g. through vacuum insulators, etc…), or
b) circumvent deleterious mechanisms intrinsic to conventional geometries (e.g.
through alternative geometries and or vacuum or normal metal or constriction
barriers)
– Fabrication techniques providing superior materials and reproducibility
– Fabrication quality of electrodes, including the effects of rough edges
– Chamber(s) characterization (e.g., temperature, gases, other materials in the
chamber) for depositing films and oxidation for fabricating reproducible high
quality qubits
– New concepts in materials and fabrication techniques or qubit designs
Any combination of the above and or additional topics may be included in a given
proposal. In general, for all topics pursued in advanced materials and fabrication
methods, proposals should focus on developing materials advances, fabrication
techniques, and junction or qubit designs that will substantially eliminate
decoherence mechanisms and significantly improve qubit performance.