Padawer-Blatt, A.; Ducatel, J.; Korkusinski, M.; Bogan, A.; Gaudreau, L.; Zawadzki, P.; Austing, D.G.; Sachrajda, A.S.; Studenikin, S.; Tracy, Lisa A.; Reno, J.; Hargett, Terry H.
Difference in g factors in multidot structures can form the basis of dot-selective spin manipulation under global microwave irradiation. Employing electric dipole spin resonance facilitated by strong spin-orbit interaction (SOI), we observe differences in the extracted values of the single-hole effective g factors of the constituent quantum dots of a GaAs/AlGaAs double quantum dot device at the level of ∼5%-10%. We examine the continuous change in the hole g factor with electrical detuning over a wide range of interdot tunnel couplings and for different out-of-plane magnetic fields. The observed tendency of the quantum dot effective g factors to steadily increase on decreasing the interdot coupling or on increasing the magnetic field is attributed to the impact on the SOI of changing the dot confinement potential and heavy-hole light-hole mixing.
Padawer-Blatt, Aviv P.; Ducatel, Jordan D.; Bogan, Alex B.; Austing, Guy D.; Gaudreau, Louis G.; Zawadzki, Piotr Z.; Sachrajda, Andrew S.; Studenikin, Sergei S.; Tracy, Lisa A.; Reno, John R.; Hargett, Terry H.
Bogan, Alex; Studenikin, Sergei; Korkusinski, Marek; Gaudreau, Louis; Phoenix, Jason; Zawadzki, Piotr; Sachrajda, Andy; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
We analyze experimentally and theoretically the transport spectra of a gated lateral GaAs double quantum dot containing two holes. The strong spin-orbit interaction present in the hole subband lifts the Pauli spin blockade and allows to map out the complete spectra of the two-hole system. By performing measurements in both source-drain voltage directions, at different detunings and magnetic fields, we carry out quantitative fitting to a Hubbard two-site model accounting for the tunnel coupling to the leads and the spin-flip relaxation process. We extract the singlet-triplet gap and the magnetic field corresponding to the singlet-triplet transition in the double-hole ground state. Additionally, at the singlet-triplet transition we find a resonant enhancement (in the blockaded direction) and suppression of current (in the conduction direction). The current enhancement stems from the multiple resonance of two-hole levels, opening several conduction channels at once. The current suppression arises from the quantum interference of spin-conserving and spin-flipping tunneling processes.
We report a detailed study of the tunnel barriers within a single-hole GaAs/AlGaAs double quantum dot device (DQD). For quantum information applications as well as fundamental studies, careful tuning and reliable measurements of the barriers are important requirements. In order to tune a DQD device adequately into the single-hole electric dipole spin resonance regime, one has to employ a variety of techniques to cover the extended range of tunnel couplings. In this work, we demonstrate four separate techniques, based upon charge sensing, quantum transport, time-resolved pulsing, and electron dipole spin resonance spectroscopy to determine the couplings as a function of relevant gate voltages and magnetic field. Measurements were performed under conditions of both symmetric and asymmetric tunnel couplings to the leads. Good agreement was observed between different techniques when measured under the same conditions. The results indicate that even in this relatively simple circuit, the requirement to tune multiple gates and the consequences of real potential profiles result in non-intuitive dependencies of the couplings as a function of the plunger gate voltage and the magnetic field.
There is rapidly expanding interest in exploiting the spin of valence-band holes rather than conduction-band electrons for spin qubit semiconductor circuits composed of coupled quantum dots. The hole platform offers stronger spin-orbit interaction (SOI), large difference between in-dot-plane and out-of-dot-plane g-factors, i.e. g-factor anisotropy, and a significantly reduced hyperfine coupling to nuclei in the host material. These attributes collectively can deliver fast all-electric coherent spin manipulation, efficient spin-flip inter-dot tunneling channels, a voltage tunable effective g-factor, a g-factor adjustable to nearly zero in an appropriately oriented external magnetic field, and long spin relaxation and coherence times. Here, we review our recent work on the physics of heavy holes confined in a planar GaAs/AlGaAs double quantum dot system with strong SOI. For a single-hole, we have performed resonant tunneling magneto-spectroscopy to extract spin-flip and spin-conserving tunneling strengths, implemented spin-flip Landau-Zener-Stückelberg-Majorana (LZSM) interferometry, determined the spin relaxation time T 1 as a function of magnetic field using a fast single-shot latched charge technique, electrically tuned the effective g-factor revealed by electric dipole spin resonance, and found signatures of the hyperfine interaction and dynamic nuclear polarization with holes. For two-holes, we have measured the energy spectrum in the presence of strong SOI (and so not limited by Pauli spin blockade), quantified the heavy-hole (HH) g-factor anisotropy on tilting the magnetic field, described a scheme to employ HHs whose g-factor is tunable to nearly zero for an in-plane magnetic field for a coherent photon-to-spin interface, and observed a well-defined LZSM interference pattern at small magnetic fields on pulsing through the singlet-triplet anti-crossing.
Studenikin, Sergei S.; Korkusinski, Marek K.; Austing, Guy D.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Sachrajda, Andy S.; Ducatel, Jordan D.; Padawer-Blatt, Aviv P.; Bogan, Alex B.; Takahashi, Motoi T.; Coish, Bill C.; Philippopoulos, Pericles P.; Hirayama, Yoshiro H.; Reno, J.L.; Tracy, Lisa A.; Hargett, Terry H.
Studenikin, Sergei S.; Austing, Guy D.; Sachrajda, Andrew S.; Ducatel, Jordan D.; Padawer-Blatt, Aviv P.; Bogan, Alex B.; Takahashi, Motoi T.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.; Coish, Bill C.; Philippopoulos, Pericles P.
Sachrajda, Andrew S.; Studenikin, Sergei S.; Austing, Guy D.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Bogan, Alex B.; Takahashi, Motoi T.; Ducatel, Jordan D.; Padawer-Blatt, Aviv P.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Hole spins have recently emerged as attractive candidates for solid-state qubits for quantum computing. Their state can be manipulated electrically by taking advantage of the strong spin-orbit interaction (SOI). Crucially, these systems promise longer spin coherence lifetimes owing to their weak interactions with nuclear spins as compared to electron spin qubits. Here we measure the spin relaxation time T1 of a single hole in a GaAs gated lateral double quantum dot device. We propose a protocol converting the spin state into long-lived charge configurations by the SOI-assisted spin-flip tunneling between dots. By interrogating the system with a charge detector we extract the magnetic-field dependence of T1 ∝ B−5 for fields larger than B = 0.5 T, suggesting the phonon-assisted Dresselhaus SOI as the relaxation channel. This coupling limits the measured values of T1 from ~400 ns at B = 1.5 T up to ~60 μs at B = 0.5 T.
Takahashi, Motoi T.; Studenikin, Sergei S.; Austing, Guy D.; Bogan, Alex B.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Tracy, Lisa A.; Hargett, Terry H.; Reno, J.L.; Sachrajda, Andrew S.
Studenikin, Sergei S.; Austing, Guy D.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Bogan, Alex B.; Ducatel, Jordan D.; Padawder-Blatt, Aviv P.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Studenikin, Sergei S.; Bogan, Alex B.; Takahashi, Motoi T.; Austing, Guy D.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Sachrajda, Andy S.; Tracy, Lisa A.; Hargett, Terry H.; Reno, J.L.
Sachrajda, Andrew S.; Bogan, Alex B.; Studenikin, Sergei S.; Gaudreau, Louis G.; Takahashi, Motoi T.; Austing, Guy D.; Korkusinski, Marek K.; Ares, Geof A.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
We demonstrate ultra-low power cryogenic high electron mobility transistor (HEMT) amplifiers for measurement of quantum devices. The low power consumption (few uWs) allows the amplifier to be located near the device, at the coldest cryostat stage (typically less than 100 mK). Such placement minimizes parasitic capacitance and reduces the impact of environmental noise (e.g. triboelectric noise in cabling), allowing for improvements in measurement gain, bandwidth and noise. We use custom high electron mobility transistors (HEMTs) in GaAs/A1GaAs heterostructures. These HEMTs are known to have excellent performance specifically at mK temperatures, with electron mobilities that can exceed 10 6 cm 2 /Vs, allowing for large gain with low power consumption. Low temperature measurements of custom HEMT amplifiers at T = 4 K show a current sensitivity of 50 pA at 1 MHz bandwidth for 5 mW power dissipation, which is an improvement upon performance of amplifiers using off-the-shelf HEMTs.
Sachrajda, Andrew S.; Bogan, Alex B.; Studenikin, Sergei S.; Gaudreau, Louis G.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.; Korkusinski, Marek K.; Aers, Geof A.
We perform Landau-Zener-Stückelberg-Majorana (LZSM) spectroscopy on a system with strong spin-orbit interaction (SOI), realized as a single hole confined in a gated double quantum dot. Analogous to electron systems, at a magnetic field B=0 and high modulation frequencies, we observe photon-assisted tunneling between dots, which smoothly evolves into the typical LZSM funnel-shaped interference pattern as the frequency is decreased. In contrast to electrons, the SOI enables an additional, efficient spin-flip interdot tunneling channel, introducing a distinct interference pattern at finite B. Magnetotransport spectra at low-frequency LZSM driving show the two channels to be equally coherent. High-frequency LZSM driving reveals complex photon-assisted tunneling pathways, both spin conserving and spin flip, which form closed loops at critical magnetic fields. In one such loop, an arbitrary hole spin state is inverted, opening the way toward its all-electrical manipulation.
Studenikin, Sergei S.; Bogan, Alex B.; Gaudreau, Louis G.; Korkusinski, Marek K.; Zawadski, Piotr Z.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.; Sachrajda, Andrew S.
Sachrajda, Andrew S.; Bogan, Alex B.; Studenikin, Alex S.; Korkusinski, Marek K.; Aers, Geoff A.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Korkusinski, Marek K.; Bogan, Alex B.; Studenikin, Sergei S.; Aers, Geoff A.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Sachrajda, Andrew S.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Sachrajda, Andrew S.; Bogan, Alex B.; Studenikin, Sergei S.; Korkusinski, Marek K.; Aers, Geoff A.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Korkusinski, Marek K.; Bogan, Alex B.; Studeinkin, Sergei S.; Aers, Geoff A.; Gaudreau, Louis G.; Zawadski, Piotr Z.; Sachrajda, Andrew S.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Bogan, Alex B.; Studenikin, Sergei S.; Gaudreau, Louis G.; Korkusinski, Marek K.; Aers, Geof A.; Zawadski, Piotr Z.; Sachrajda, Andrew S.; Tracy, Lisa A.; Reno, J.L.; Hargett, Terry H.
Most spin qubit research to date has focused on manipulating single electron spins in quantum dots. However, hole spins are predicted to have some advantages over electron spins, such as reduced coupling to host semiconductor nuclear spins and the ability to control hole spins electrically using the large spin-orbit interaction. Building on recent advances in fabricating high-mobility 2D hole systems in GaAs/AlGaAs heterostructures at Sandia, we fabricate and characterize single hole transistors in GaAs. We demonstrate p-type double quantum dot devices with few-hole occupation, which could be used to study the physics of individual hole spins and control over coupling between hole spins, looking towards eventual applications in quantum computing. Intentionally left blank
This report describes the research accomplishments achieved under the LDRD Project ''Leaky-mode VCSELs for photonic logic circuits''. Leaky-mode vertical-cavity surface-emitting lasers (VCSELs) offer new possibilities for integration of microcavity lasers to create optical microsystems. A leaky-mode VCSEL output-couples light laterally, in the plane of the semiconductor wafer, which allows the light to interact with adjacent lasers, modulators, and detectors on the same wafer. The fabrication of leaky-mode VCSELs based on effective index modification was proposed and demonstrated at Sandia in 1999 but was not adequately developed for use in applications. The aim of this LDRD has been to advance the design and fabrication of leaky-mode VCSELs to the point where initial applications can be attempted. In the first and second years of this LDRD we concentrated on overcoming previous difficulties in the epitaxial growth and fabrication of these advanced VCSELs. In the third year, we focused on applications of leaky-mode VCSELs, such as all-optical processing circuits based on gain quenching.
This report describes the research accomplishments achieved under the LDRD Project 'Radiation Hardened Optoelectronic Components for Space-Based Applications.' The aim of this LDRD has been to investigate the radiation hardness of vertical-cavity surface-emitting lasers (VCSELs) and photodiodes by looking at both the effects of total dose and of single-event upsets on the electrical and optical characteristics of VCSELs and photodiodes. These investigations were intended to provide guidance for the eventual integration of radiation hardened VCSELs and photodiodes with rad-hard driver and receiver electronics from an external vendor for space applications. During this one-year project, we have fabricated GaAs-based VCSELs and photodiodes, investigated ionization-induced transient effects due to high-energy protons, and measured the degradation of performance from both high-energy protons and neutrons.
GaAsSbN was grown by organometallic vapor phase epitaxy (OMVPE) as an alternative material to InGaAsN for long wavelength emission on GaAs substrates. OMVPE of GaAsSbN using trimethylgallium, 100% arsine, trimethylantimony, and 1,1-dimethylhydrazine was found to be kinetically limited at growth temperatures ranging from 520 C to 600 C, with an activation energy of 10.4 kcal/mol. The growth rate was linearly dependent on the group III flow and has a complex dependence on the group V constituents. A room temperature photoluminescence wavelength of >1.3 {micro}m was observed for unannealed GaAs{sub 0.69}Sb{sub 0.3}N{sub 0.01}. Low temperature (4 K) photoluminescence of GaAs{sub 0.69}Sb{sub 0.3}N{sub 0.01} shows an increase in FWHM of 2.4-3.4 times the FWHM of GaAs{sub 0.7}Sb{sub 0.3}, a red shift of 55-77 meV, and a decrease in intensity of one to two orders of magnitude. Hall measurements indicate a behavior similar to that of InGaAsN, a 300 K hole mobility of 350 cm{sup 2}/V-s with a 1.0 x 10{sup 17}/cm{sup 3} background hole concentration, and a 77 K mobility of 1220 cm{sup 2}/V-s with a background hole concentration of 4.8 x 10{sup 16}/cm{sup 3}. The hole mass of GaAs{sub 0.7}Sb{sub 0.3}/GaAs heterostructures was estimated at 0.37-0.40m{sub o}, and we estimate an electron mass of 0.2-0.3m{sub o} for the GaAs{sub 0.69}Sb{sub 0.3}N{sub 0.01}/GaAs system. The reduced exciton mass for GaAsSbN was estimated at about twice that found for GaAsSb by a comparison of diamagnetic shift vs. magnetic field.
This report describes the research accomplishments achieved under the LDRD Project ''High-Bandwidth Optical Data Interconnects for Satellite Applications.'' The goal of this LDRD has been to address the future needs of focal-plane-array (FPA) sensors by exploring the use of high-bandwidth fiber-optic interconnects to transmit FPA signals within a satellite. We have focused primarily on vertical-cavity surface-emitting laser (VCSEL) based transmitters, due to the previously demonstrated immunity of VCSELs to total radiation doses up to 1 Mrad. In addition, VCSELs offer high modulation bandwidth (roughly 10 GHz), low power consumption (roughly 5 mW), and high coupling efficiency (greater than -3dB) to optical fibers. In the first year of this LDRD, we concentrated on the task of transmitting analog signals from a cryogenic FPA to a remote analog-to-digital converter. In the second year, we considered the transmission of digital signals produced by the analog-to-digital converter to a remote computer on the satellite. Specifically, we considered the situation in which the FPA, analog-to-digital converter, and VCSEL-based transmitter were all cooled to cryogenic temperatures. This situation requires VCSELs that operate at cryogenic temperature, dissipate minimal heat, and meet the electrical drive requirements in terms of voltage, current, and bandwidth.
Rotation sensors (gyros) and accelerometers are essential components for all precision-guided weapons and autonomous mobile surveillance platforms. MEMS gyro development has been based primarily on the properties of moving mass to sense rotation and has failed to keep pace with the concurrent development of MEMS accelerometers because the reduction of size and therefore mass is substantially more detrimental to the performance of gyros than to accelerometers. A small ({approx}0.2 cu in), robust ({approx}20,000g), inexpensive ({approx}$500), tactical grade performance ({approx}10-20 deg/hr.) gyro is vital for the successful implementation of the next generation of ''smart'' weapons and surveillance apparatus. The range of applications (relevant to Sandia's mission) that are substantially enhanced in capability or enabled by the availability of a gyro possessing the above attributes includes nuclear weapon guidance, fuzing, and safing; synthetic aperture radar (SAR) motion compensation; autonomous air and ground vehicles; gun-launched munitions; satellite control; and personnel tracking. For example, a gyro of this capability would open for consideration more fuzing options for earth-penetration weapons. The MEMS gyros currently available are lacking in one or more of the aforementioned attributes. An integrated optical gyro, however, possesses the potential of achieving all desired attributes. Optical gyros use the properties of light to sense rotation and require no moving mass. Only the individual optical elements required for the generation, detection, and control of light are susceptible to shock. Integrating these elements immensely enhances the gyro's robustness while achieving size and cost reduction. This project's goal, a joint effort between organizations 2300 and 1700, was to demonstrate an RMOG produced from a monolithic photonic integrated circuit coupled with a SiON waveguide resonator. During this LDRD program, we have developed the photonic elements necessary for a resonant micro-optical gyro. We individually designed an AlGaAs distributed Bragg reflector laser; GaAs phase modulator and GaAs photodiode detector. Furthermore, we have fabricated a breadboard gyroscope, which was used to confirm modeling and evaluate signal processing and control circuits.