Silicon is more than the dominant material in the conventional microelectronics industry: it also has potential as a host material for emerging quantum information technologies. Standard fabrication ...techniques already allow the isolation of single electron spins in silicon transistor-like devices. Although this is also possible in other materials, silicon-based systems have the advantage of interacting more weakly with nuclear spins. Reducing such interactions is important for the control of spin quantum bits because nuclear fluctuations limit quantum phase coherence, as seen in recent experiments in GaAs-based quantum dots. Advances in reducing nuclear decoherence effects by means of complex control still result in coherence times much shorter than those seen in experiments on large ensembles of impurity-bound electrons in bulk silicon crystals. Here we report coherent control of electron spins in two coupled quantum dots in an undoped Si/SiGe heterostructure and show that this system has a nuclei-induced dephasing time of 360 nanoseconds, which is an increase by nearly two orders of magnitude over similar measurements in GaAs-based quantum dots. The degree of phase coherence observed, combined with fast, gated electrical initialization, read-out and control, should motivate future development of silicon-based quantum information processors.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report on a quantum dot device design that combines the low disorder properties of undoped SiGe heterostructure materials with an overlapping gate stack in which each electrostatic gate has a ...dominant and unique function-control of individual quantum dot occupancies and of lateral tunneling into and between dots. Control of the tunneling rate between a dot and an electron bath is demonstrated over more than nine orders of magnitude and independently confirmed by direct measurement within the bandwidth of our amplifiers. The inter-dot tunnel coupling at the charge configuration anti-crossing is directly measured to quantify the control of a single inter-dot tunnel barrier gate. A simple exponential dependence is sufficient to describe each of these tunneling processes as a function of the controlling gate voltage.
An analytical model and supporting measured data are presented for a preamplified W-band radiometer with a zero-bias detector appropriate for commercial millimeter-wave imaging cameras. Basic ...radiometer parameters, including RF bandwidth, are computed directly from simple low-frequency measurements and compare well with those obtained from RF measurements. A detailed analytical model shows how radiometer performance depends on internal component parameters, such as low-noise amplifier gain, noise factor, reflection coefficient, detector responsivity, etc. The measurements suggest that performance is sufficient for operation without a Dicke switch or mechanical chopping. A measured noise equivalent temperature difference of 0.45 K was obtained, assuming a single sensor is scanned across a focal plane, forming 32 pixels with 3.125-ms integration time per pixel. This sensitivity is considered sufficient by commercial manufacturers to obtain quality images in low-contrast (e.g., indoor) environments.
A W-band monolithic microwave integrated circuit (MMIC), including an Sb-heterostructure diode on a GaAs substrate, has been demonstrated. The MMIC also includes the RF choke and output shorting ...capacitor essential to detector circuits. Additional input matching has yielded peak sensitivities on the order of 10 000 V/W and equivalent bandwidths of 40 GHz. Using these circuits in conjunction with current W-band low-noise amplifier technology can achieve the sub-1degK noise equivalent temperature difference necessary for producing discernible images with W-band passive imaging cameras.
Static dividers in 135-GHz InP-DHBT technology have been designed, fabricated, and measured. Circuits are operational from dc to 100 GHz. Due to limitations in available measurement equipment, ...adequate investigation of the circuit operation beyond 100 GHz is not possible at this time, however, to the authors' knowledge, this is already the highest toggling frequency reported in any static circuit in any technology. The circuit has a total area of 675/spl times/900 /spl mu/m/sup 2/, with the core of the flip-flop occupying about 240/spl times/170 /spl mu/m/sup 2/.
80-GHz differential VCO in InP SHBTs Zhihao Lao; Jensen, J.; Guinn, K. ...
IEEE microwave and wireless components letters,
09/2004, Letnik:
14, Številka:
9
Journal Article
Recenzirano
A high frequency millimeter-wave voltage-controlled oscillator (VCO) has been designed, manufactured and tested in InP single heterojunction bipolar transistor technology. The fully integrated ...fundamental differential VCO features high operating frequency up to 80 GHz with low phase noise about -118 dBc/Hz at 1-MHz offset and 5% tuning range. The VCO consumes only 95-mW power at a power supply of -5 V, while providing -2 dBm single-ended output power and 1 dBm for differential output power. The die size is 0.28 mm/sup 2/.
Both compound semiconductor and silicon-based bipolar junction transistors or heterojunction bipolar transistors (HBTs) require the efficient removal of heat in order to achieve a maximum level of ...performance and reliability. In order to satisfy both of these criteria, the electrothermal behavior of each device must be captured in a compact model. The model parameter that determines the junction temperature is R TH , the thermal resistance. Experimental methods to determine R TH often require a relatively small device with a large R TH to be attached to a set of relatively large metal pads with a low R TH . The pads act as a thermal shunt to the substrate and artificially lower the measured R TH . In order to obtain a suitable R TH value for a device located in an IC, the pads must be deembedded from the measured data, much like pad deembedding for an S-parameter measurement. Test structures with various width metal traces between the emitter pad and device's emitter have been fabricated in a 200-GHz InP double HBT process. A method of using the measured R TH of these structures and a simple resistive network model to deembed the pads is presented. It is shown that deembedded values can be as much as 30% higher than the measured R TH
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