Software for Quantum Device Design

The Microscopic Simulation of Noise

We know that noise is the primary reason information is lost in quantum devices whether those devices be sensors, quantum memory, or quantum computers. Solve the problem of noise, and the quantum devices of tomorrow become available today.

Backed by over 20 years of extensive research, our software reduces the need for guesswork in specifications and makes trial-and-error testing no longer standard procedure. Our current offerings include software for both optoelectronic devices (CADtronics) and quantum sensors (qNoise). CADtronics software was used by researchers for the detector and laser simulations below. Our qNoise software follows the same methodology as used in the spin center simulation described below.

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Superlattice design for low noise detectors

Case 1: Applied Physics Letters 105, 022107 (2014)
Full Article

The electronic structure of an InAs/InAsSb superlattice was calculated for five structures with different layer thicknesses but the same band gap. These electronic structures were used to predict different recombination rates via carrier-carrier scattering (Auger rates) for the superlattices, which were verified experimentally in the same publication.

 Case 2: Journal of Applied Physics 119, 215705 (2016)
Full Article

The electronic structure of seven InAs/InAsSb superlattices was calculated to optimize the recombination rates via carrier-carrier scattering (Auger rates). These superlattices had recombination rate trends that agreed with the predictions, described in the same publication.

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Laser active region design for efficient lasing in the mid infrared

Journal of Applied Physics 89, 3286 (2001)
Full Article

A mid-infrared laser active region based on a highly optimized InAs/GaInSb/AlAsSb quantum well was proposed that provided miniband carrier injection regions and extraction regions along with very high material gain per unit recombination current. This active region was designed to be placed in a separate confinement region to maximize the mode and the structure has been predicted to permit lasing from a single quantum well.

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Simulation of charge noise effects on a spin center's optical transition line width

PRX Quantum 2, 040310 (2021)
Full Article

This figure shows the structure of a 4H-SiC pin diode with a single optically-active spin center (divacancy). In this work the divacancy’s optical linewidth’s dependence on nearby carrier density was calculated and compared with measurements in Science 366, 1225 (2019), providing excellent agreement with no adjustable parameters. The origin of the linewidth was fluctuating charges either nearby to the spin center or in the contacts of the device. The shift in optical emission frequency as a function of voltage was calculated and provided a direct indication of the depth of the spin center in the diode. The effect of these charge fluctuations on the spin center’s coherence time was calculated and shown to be negligible compared with other mechanisms for the observed spin centers in the 2019 Science measurements.

QuantCAD Simulations & Photodetectors

Photodetectors work by detecting the presence of an electron that was excited by light, so the minimum excitation  energy (band gap) sets the maximum wavelength of light the detector is sensitive to. 

The electrons excited by light can lose their excitation energy by transferring it to many other excitations within the superlattice and eventually to heat. 

The rate at which this happens determines noise in a superlattice photodetector and is calculated by QuantCAD’s software. It is also possible to predict these rates, and thus the noise, as the material composition and structure is changed, pointing the way to device optimization

qNoise & Quantum repeaters

Quantum repeaters require the integration of single-photon sources with quantum memories. To not interfere with each other two single-photon sources should emit at distinct optical frequencies. 

Localized spin centers in semiconductors can serve as efficient single-photon sources, however their emission frequency can change depending on the electric fields and charges nearby.

If the emission frequency changes too much then it is no longer possible to distinguish a particular single-photon emitter from another. The extent of this frequency change is called the linewidth and depends on the characteristics of the environment.

QuantCAD’s software qNoise calculates the linewidth of single-photon emitters in semiconductors and how that depends on the environment. By modifying the nearby charge density, and the distance to electrical contacts, optimization of the linewidth is possible. Furthermore the emission frequency can be changed by an electric field applied to the semiconductor device. QuantCAD’s software calculates the frequency shift in a realistic semiconductor diode.

CADtronics & Lasers

Lasers work by transferring the energy of injected electrons into coherent light.

For this to be efficient that energy can’t be wasted by transferring it to other electrons within the semiconductor.  There is also the potential for the emitted light to be reabsorbed by the semiconductor. 

 For a laser to work more light has to be generated than absorbed - this is referred to as negative absorption, or gain. 

QuantCAD’s software CADtronics calculates the gain of laser active regions and also the efficiency with which light is emitted. By modifying the composition and structure of the laser active region, and calculating the gain and efficiency, optimization of lasers for various applications can be achieved.