17 research outputs found
Observation of Josephson harmonics in tunnel junctions
Approaches to developing large-scale superconducting quantum
processors must cope with the numerous microscopic degrees of freedom
that are ubiquitous in solid-state devices. State-of-the-art superconducting
qubits employ aluminium oxide (AlO) tunnel Josephson junctions as
the sources of nonlinearity necessary to perform quantum operations.
Analyses of these junctions typically assume an idealized, purely sinusoidal
currentâphase relation. However, this relation is expected to hold only in the
limit of vanishingly low-transparency channels in the AlO barrier. Here we
show that the standard currentâphase relation fails to accurately describe
the energy spectra of transmon artificial atoms across various samples
and laboratories. Instead, a mesoscopic model of tunnelling through
an inhomogeneous AlO barrier predicts percent-level contributions
from higher Josephson harmonics. By including these in the transmon
Hamiltonian, we obtain orders of magnitude better agreement between
the computed and measured energy spectra. The presence and impact of
Josephson harmonics has important implications for developing AlOx-based
quantum technologies including quantum computers and parametric
amplifiers. As an example, we show that engineered Josephson harmonics
can reduce the charge dispersion and associated errors in transmon qubits
by an order of magnitude while preserving their anharmonicity
Observation of Josephson Harmonics in Tunnel Junctions
Superconducting quantum processors have a long road ahead to reach
fault-tolerant quantum computing. One of the most daunting challenges is taming
the numerous microscopic degrees of freedom ubiquitous in solid-state devices.
State-of-the-art technologies, including the world's largest quantum
processors, employ aluminum oxide (AlO) tunnel Josephson junctions (JJs) as
sources of nonlinearity, assuming an idealized pure current-phase
relation (CR). However, this celebrated CR is
only expected to occur in the limit of vanishingly low-transparency channels in
the AlO barrier. Here we show that the standard CR fails to
accurately describe the energy spectra of transmon artificial atoms across
various samples and laboratories. Instead, a mesoscopic model of tunneling
through an inhomogeneous AlO barrier predicts %-level contributions from
higher Josephson harmonics. By including these in the transmon Hamiltonian, we
obtain orders of magnitude better agreement between the computed and measured
energy spectra. The reality of Josephson harmonics transforms qubit design and
prompts a reevaluation of models for quantum gates and readout, parametric
amplification and mixing, Floquet qubits, protected Josephson qubits, etc. As
an example, we show that engineered Josephson harmonics can reduce the charge
dispersion and the associated errors in transmon qubits by an order of
magnitude, while preserving anharmonicity
Early Developing Pig Embryos Mediate Their Own Environment in the Maternal Tract
The maternal tract plays a critical role in the success of early embryonic development providing an optimal environment for establishment and maintenance of pregnancy. Preparation of this environment requires an intimate dialogue between the embryo and her mother. However, many intriguing aspects remain unknown in this unique communication system. To advance our understanding of the process by which a blastocyst is accepted by the endometrium and better address the clinical challenges of infertility and pregnancy failure, it is imperative to decipher this complex molecular dialogue. The objective of the present work is to define the local response of the maternal tract towards the embryo during the earliest stages of pregnancy. We used a novel in vivo experimental model that eliminated genetic variability and individual differences, followed by Affymetrix microarray to identify the signals involved in this embryo-maternal dialogue. Using laparoscopic insemination one oviduct of a sow was inseminated with spermatozoa and the contralateral oviduct was injected with diluent. This model allowed us to obtain samples from the oviduct and the tip of the uterine horn containing either embryos or oocytes from the same sow. Microarray analysis showed that most of the transcripts differentially expressed were down-regulated in the uterine horn in response to blastocysts when compared to oocytes. Many of the transcripts altered in response to the embryo in the uterine horn were related to the immune system. We used an in silico mathematical model to demonstrate the role of the embryo as a modulator of the immune system. This model revealed that relatively modest changes induced by the presence of the embryo could modulate the maternal immune response. These findings suggested that the presence of the embryo might regulate the immune system in the maternal tract to allow the refractory uterus to tolerate the embryo and support its development
mtDNA analysis of Nile River Valley populations: A genetic corridor or a barrier to migration?
To assess the extent to which the Nile River Valley has been a corridor for human migrations between Egypt and sub-Saharan Africa, we analyzed mtDNA variation in 224 individuals from various locations along the river. Sequences of the first hypervariable segment (HV1) of the mtDNA control region and a polymorphic HpaI site at position 3592 allowed us to designate each mtDNA as being of "northern" or "southern" affiliation. Proportions of northern and southern mtDNA differed significantly between Egypt, Nubia, and the southern Sudan. At slowly evolving sites within HV1, northern-mtDNA diversity was highest in Egypt and lowest in the southern Sudan, and southern-mtDNA diversity was highest in the southern Sudan and lowest in Egypt, indicating that migrations had occurred bidirectionally along the Nile River Valley. Egypt and Nubia have low and similar amounts of divergence for both mtDNA types, which is consistent with historical evidence for long-term interactions between Egypt and Nubia. Spatial autocorrelation analysis demonstrates a smooth gradient of decreasing genetic similarity of mtDNA types as geographic distance between sampling localities increases, strongly suggesting gene flow along the Nile, with no evident barriers. We conclude that these migrations probably occurred within the past few hundred to few thousand years and that the migration from north to south was either earlier or lesser in the extent of gene flow than the migration from south to north
Observation of Josephson Harmonics in Tunnel Junctions
Superconducting quantum processors have a long road ahead to reach fault-tolerant quantum computing. One of the most daunting challenges is taming the numerous microscopic degrees of freedom ubiquitous in solid-state devices. State-of-the-art technologies, including the world's largest quantum processors, employ aluminum oxide (AlO) tunnel Josephson junctions (JJs) as sources of nonlinearity, assuming an idealized pure current-phase relation (CR). However, this celebrated CR is only expected to occur in the limit of vanishingly low-transparency channels in the AlO barrier. Here we show that the standard CR fails to accurately describe the energy spectra of transmon artificial atoms across various samples and laboratories. Instead, a mesoscopic model of tunneling through an inhomogeneous AlO barrier predicts %-level contributions from higher Josephson harmonics. By including these in the transmon Hamiltonian, we obtain orders of magnitude better agreement between the computed and measured energy spectra. The reality of Josephson harmonics transforms qubit design and prompts a reevaluation of models for quantum gates and readout, parametric amplification and mixing, Floquet qubits, protected Josephson qubits, etc. As an example, we show that engineered Josephson harmonics can reduce the charge dispersion and the associated errors in transmon qubits by an order of magnitude, while preserving anharmonicity
Observation of Josephson Harmonics in Tunnel Junctions
Superconducting quantum processors have a long road ahead to reach fault-tolerant quantum computing. One of the most daunting challenges is taming the numerous microscopic degrees of freedom ubiquitous in solid-state devices. State-of-the-art technologies, including the world's largest quantum processors, employ aluminum oxide (AlO) tunnel Josephson junctions (JJs) as sources of nonlinearity, assuming an idealized pure current-phase relation (CR). However, this celebrated CR is only expected to occur in the limit of vanishingly low-transparency channels in the AlO barrier. Here we show that the standard CR fails to accurately describe the energy spectra of transmon artificial atoms across various samples and laboratories. Instead, a mesoscopic model of tunneling through an inhomogeneous AlO barrier predicts %-level contributions from higher Josephson harmonics. By including these in the transmon Hamiltonian, we obtain orders of magnitude better agreement between the computed and measured energy spectra. The reality of Josephson harmonics transforms qubit design and prompts a reevaluation of models for quantum gates and readout, parametric amplification and mixing, Floquet qubits, protected Josephson qubits, etc. As an example, we show that engineered Josephson harmonics can reduce the charge dispersion and the associated errors in transmon qubits by an order of magnitude, while preserving anharmonicity