53 research outputs found

    Single spin universal Boolean logic

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    Recent advances in manipulating single electron spins in quantum dots have brought us close to the realization of classical logic gates based on representing binary bits in spin polarizations of single electrons. Here, we show that a linear array of three quantum dots, each containing a single spin polarized electron, and with nearest neighbor exchange coupling, acts as the universal NAND gate. The energy dissipated during switching this gate is the Landauer-Shannon limit of kTln(1/p) [T = ambient temperature and p = intrinsic gate error probability]. With present day technology, p = 1E-9 is achievable above 1 K temperature. Even with this small intrinsic error probability, the energy dissipated during switching the NAND gate is only ~ 21 kT, while today's nanoscale transistors dissipate about 40,000 - 50,000 kT when they switch

    Алгоритм опрСдСлСния ΠΎΠΏΡ‚ΠΈΠΌΠ°Π»ΡŒΠ½ΠΎΠ³ΠΎ числа Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ ΠΈΡΠΏΠΎΠ»ΡŒΠ·ΡƒΠ΅ΠΌΡ‹Ρ… ΠΏΡ€ΠΈ Π²Π½ΡƒΡ‚Ρ€ΠΈΡ‚ΠΊΠ°Π½Π΅Π²ΠΎΠΉ фотодинамичСской Ρ‚Π΅Ρ€Π°ΠΏΠΈΠΈ Ρ€Π°ΠΊΠ° ΠΌΠΎΠ»ΠΎΡ‡Π½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ‹ Π½Π° основании Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ уравнСния

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    It is essential in interstitial Photodynamic therapy (iPDT) treatment planning to ensure a homogeneous distribution within a tumor volume using cylindrical diffusing fibers while keeping the surrounding tissue intact. Light distribution is simulated through two algorithms based on the diffusion equation assuming diffusers as light sources. The first algorithm analyzes the diffusion equation and studies the effects of different variables (optical properties, delivered power, diffuser length, and position). Next, optical properties of breast were applied to estimate the volume that receives accepted light dose from one diffuser. In the second algorithm, multiple diffusers were simulated in order to find the relation between the volume and the number of required diffusers which are needed to cover cubical or cylindrical volume with sufficient light dose. Throughout this study, real values of optical properties, clinical laser power, and treatment time were considered to evaluate sufficient light doses. This study is in agreement with previous works in that optical properties are the major factors influencing light distribution in iPDT. It is shown that for a homogeneous phantom mimicking breast cancer and cubical or cylindrical shape, the number of required fibers N equal WΓ—L or D2 respectively.ΠŸΡ€ΠΈ ΠΏΠ»Π°Π½ΠΈΡ€ΠΎΠ²Π°Π½ΠΈΠΈ Π²Π½ΡƒΡ‚Ρ€ΠΈΡ‚ΠΊΠ°Π½Π΅Π²ΠΎΠΉ фотодинамичСской Ρ‚Π΅Ρ€Π°ΠΏΠΈΠΈ (iPDT ) с использованиСм цилиндричСских Π΄ΠΈΡ„Ρ„ΡƒΠ·Π½Ρ‹Ρ… Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ Π²Π°ΠΆΠ½ΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅Ρ‡ΠΈΡ‚ΡŒ ΠΎΠ΄Π½ΠΎΡ€ΠΎΠ΄Π½ΠΎΠ΅ распрСдСлСниС свСта ΠΏΠΎ всСму ΠΎΠ±ΡŠΠ΅ΠΌΡƒ ΠΎΠΏΡƒΡ…ΠΎΠ»ΠΈ, сохранив ΠΏΡ€ΠΈ этом Ρ†Π΅Π»ΠΎΡΡ‚Π½ΠΎΡΡ‚ΡŒ ΠΎΠΊΡ€ΡƒΠΆΠ°ΡŽΡ‰Π΅ΠΉ Ρ‚ΠΊΠ°Π½ΠΈ. Авторы Π΄Π°Π½Π½ΠΎΠΉ ΡΡ‚Π°Ρ‚ΡŒΠΈ смодСлировали распрСдСлСниС свСта с ΠΏΠΎΠΌΠΎΡ‰ΡŒΡŽ Π΄Π²ΡƒΡ… Π°Π»Π³ΠΎΡ€ΠΈΡ‚ΠΌΠΎΠ², основанных Π½Π° ΡƒΡ€Π°Π²Π½Π΅Π½ΠΈΠΈ Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΈΠΈ, Π² ΠΊΠΎΡ‚ΠΎΡ€Ρ‹Ρ… Π² качСствС источников свСта ΠΈΡΠΏΠΎΠ»ΡŒΠ·ΡƒΡŽΡ‚ΡΡ цилиндричСскиС Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΎΡ€Ρ‹. ΠŸΠ΅Ρ€Π²Ρ‹ΠΉ Π°Π»Π³ΠΎΡ€ΠΈΡ‚ΠΌ Π°Π½Π°Π»ΠΈΠ·ΠΈΡ€ΡƒΠ΅Ρ‚ ΡƒΡ€Π°Π²Π½Π΅Π½ΠΈΠ΅ Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΈΠΈ ΠΈ ΠΈΠ·ΡƒΡ‡Π°Π΅Ρ‚ влияниС Ρ€Π°Π·Π»ΠΈΡ‡Π½Ρ‹Ρ… ΠΏΠ΅Ρ€Π΅ΠΌΠ΅Π½Π½Ρ‹Ρ… (оптичСских свойств источника, примСняСмой мощности, Π΄Π»ΠΈΠ½Ρ‹ Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΎΡ€Π° ΠΈ Π΅Π³ΠΎ полоТСния). Π—Π°Ρ‚Π΅ΠΌ Π±Ρ‹Π»ΠΈ ΠΈΡΠΏΠΎΠ»ΡŒΠ·ΠΎΠ²Π°Π½Ρ‹ ΠΏΠ°Ρ€Π°ΠΌΠ΅Ρ‚Ρ€Ρ‹ оптичСских свойств ΠΌΠΎΠ»ΠΎΡ‡Π½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ‹ для ΠΎΡ†Π΅Π½ΠΊΠΈ объСма, ΠΊΠΎΡ‚ΠΎΡ€Ρ‹ΠΉ рассчитываСт ΡΠ²Π΅Ρ‚ΠΎΠ²ΡƒΡŽ Π΄ΠΎΠ·Ρƒ ΠΎΡ‚ ΠΎΠ΄Π½ΠΎΠ³ΠΎ Π΄ΠΈΡ„Ρ„ΡƒΠ·ΠΎΡ€Π°. Π’ΠΎ Π²Ρ‚ΠΎΡ€ΠΎΠΌ Π°Π»Π³ΠΎΡ€ΠΈΡ‚ΠΌΠ΅ Π±Ρ‹Π»ΠΎ смодСлировано нСсколько рассСиватСлСй для Π½Π°Ρ…ΠΎΠΆΠ΄Π΅ ния ΡΠΎΠΎΡ‚Π½ΠΎΡˆΠ΅Π½ΠΈΡ ΠΌΠ΅ΠΆΠ΄Ρƒ объСмом ΠΈ количСством рассСиватСлСй, Π½Π΅ΠΎΠ±Ρ…ΠΎΠ΄ΠΈΠΌΡ‹Ρ… для покрытия кубичСского ΠΈΠ»ΠΈ цилиндричСского объСма достаточной свСтовой Π΄ΠΎΠ·ΠΎΠΉ. На протяТСнии всСго этого исслСдования Ρ€Π°ΡΡΠΌΠ°Ρ‚Ρ€ΠΈΠ²Π°Π»ΠΈΡΡŒ Ρ€Π΅Π°Π»ΡŒΠ½Ρ‹Π΅ значСния оптичСских свойств, клиничСской мощности Π»Π°Π·Π΅Ρ€Π° ΠΈ Π²Ρ€Π΅ΠΌΠ΅Π½ΠΈ лСчСния для ΠΎΡ†Π΅Π½ΠΊΠΈ достаточных свСтовых Π΄ΠΎΠ·. Π­Ρ‚ΠΎ исслСдованиС согласуСтся с ΠΏΡ€Π΅Π΄Ρ‹Π΄ΡƒΡ‰ΠΈΠΌΠΈ Ρ€Π°Π±ΠΎΡ‚Π°ΠΌΠΈ Π² Ρ‚ΠΎΠΌ, Ρ‡Ρ‚ΠΎ оптичСскиС свойства ΡΠ²Π»ΡΡŽΡ‚ΡΡ основными Ρ„Π°ΠΊΡ‚ΠΎΡ€Π°ΠΌΠΈ, Π²Π»ΠΈΡΡŽΡ‰ΠΈΠΌΠΈ Π½Π° распрСдСлСниС свСта при iPDT. Показано, Ρ‡Ρ‚ΠΎ, для ΠΎΠ΄Π½ΠΎΡ€ΠΎΠ΄Π½ΠΎΠ³ΠΎ Ρ„Π°Π½Ρ‚ΠΎΠΌΠ°, ΠΈΠΌΠΈΡ‚ΠΈΡ€ΡƒΡŽΡ‰Π΅Π³ΠΎ Ρ€Π°ΠΊ ΠΌΠΎΠ»ΠΎΡ‡Π½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ‹, кубичСской ΠΈΠ»ΠΈ цилиндричСской Ρ„ΠΎΡ€ΠΌΡ‹, количСство Ρ‚Ρ€Π΅Π±ΡƒΠ΅ΠΌΡ‹Ρ… Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ N Ρ€Π°Π²Π½ΠΎ WΓ—L ΠΈΠ»ΠΈ D2 , соотвСтствСнно

    Cotunneling drag effect in Coulomb-coupled quantum dots

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    In Coulomb drag, a current flowing in one conductor can induce a voltage across an adjacent conductor via the Coulomb interaction. The mechanisms yielding drag effects are not always understood, even though drag effects are sufficiently general to be seen in many low-dimensional systems. In this Letter, we observe Coulomb drag in a Coulomb-coupled double quantum dot (CC-DQD) and, through both experimental and theoretical arguments, identify cotunneling as essential to obtaining a correct qualitative understanding of the drag behavior.Comment: Main text: 5 pages, 5 figures; SM: 11 pages, 5 figures, 1 tabl

    Spin-Dependent Tunneling of Single Electrons into an Empty Quantum Dot

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    Using real-time charge sensing and gate pulsing techniques we measure the ratio of the rates for tunneling into the excited and ground spin states of a single-electron AlGaAs/GaAs quantum dot in a parallel magnetic field. We find that the ratio decreases with increasing magnetic field until tunneling into the excited spin state is completely suppressed. However, we find that by adjusting the voltages on the surface gates to change the orbital configuration of the dot we can restore tunneling into the excited spin state and that the ratio reaches a maximum when the dot is symmetric.Comment: 4 pages, 3 figure

    Electrical control of spin relaxation in a quantum dot

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    We demonstrate electrical control of the spin relaxation time T_1 between Zeeman split spin states of a single electron in a lateral quantum dot. We find that relaxation is mediated by the spin-orbit interaction, and by manipulating the orbital states of the dot using gate voltages we vary the relaxation rate W= (T_1)^-1 by over an order of magnitude. The dependence of W on orbital confinement agrees with theoretical predictions and from these data we extract the spin-orbit length. We also measure the dependence of W on magnetic field and demonstrate that spin-orbit mediated coupling to phonons is the dominant relaxation mechanism down to 1T, where T_1 exceeds 1s.Comment: 4 pages, 3 figure
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