53 research outputs found
Single spin universal Boolean logic
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
ΠΠ»Π³ΠΎΡΠΈΡΠΌ ΠΎΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΡ ΠΎΠΏΡΠΈΠΌΠ°Π»ΡΠ½ΠΎΠ³ΠΎ ΡΠΈΡΠ»Π° Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ ΠΈΡΠΏΠΎΠ»ΡΠ·ΡΠ΅ΠΌΡΡ ΠΏΡΠΈ Π²Π½ΡΡΡΠΈΡΠΊΠ°Π½Π΅Π²ΠΎΠΉ ΡΠΎΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠ΅ΡΠ°ΠΏΠΈΠΈ ΡΠ°ΠΊΠ° ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ Π½Π° ΠΎΡΠ½ΠΎΠ²Π°Π½ΠΈΠΈ Π΄ΠΈΡΡΡΠ·ΠΈΠΎΠ½Π½ΠΎΠ³ΠΎ ΡΡΠ°Π²Π½Π΅Π½ΠΈΡ
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 WΓL or D2 respectively.ΠΡΠΈ ΠΏΠ»Π°Π½ΠΈΡΠΎΠ²Π°Π½ΠΈΠΈ Π²Π½ΡΡΡΠΈΡΠΊΠ°Π½Π΅Π²ΠΎΠΉ ΡΠΎΡΠΎΠ΄ΠΈΠ½Π°ΠΌΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠ΅ΡΠ°ΠΏΠΈΠΈ (iPDT ) Ρ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½ΠΈΠ΅ΠΌ ΡΠΈΠ»ΠΈΠ½Π΄ΡΠΈΡΠ΅ΡΠΊΠΈΡ
Π΄ΠΈΡΡΡΠ·Π½ΡΡ
Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ Π²Π°ΠΆΠ½ΠΎ ΠΎΠ±Π΅ΡΠΏΠ΅ΡΠΈΡΡ ΠΎΠ΄Π½ΠΎΡΠΎΠ΄Π½ΠΎΠ΅ ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠ΅ ΡΠ²Π΅ΡΠ° ΠΏΠΎ Π²ΡΠ΅ΠΌΡ ΠΎΠ±ΡΠ΅ΠΌΡ ΠΎΠΏΡΡ
ΠΎΠ»ΠΈ, ΡΠΎΡ
ΡΠ°Π½ΠΈΠ² ΠΏΡΠΈ ΡΡΠΎΠΌ ΡΠ΅Π»ΠΎΡΡΠ½ΠΎΡΡΡ ΠΎΠΊΡΡΠΆΠ°ΡΡΠ΅ΠΉ ΡΠΊΠ°Π½ΠΈ. ΠΠ²ΡΠΎΡΡ Π΄Π°Π½Π½ΠΎΠΉ ΡΡΠ°ΡΡΠΈ ΡΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π»ΠΈ ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠ΅ ΡΠ²Π΅ΡΠ° Ρ ΠΏΠΎΠΌΠΎΡΡΡ Π΄Π²ΡΡ
Π°Π»Π³ΠΎΡΠΈΡΠΌΠΎΠ², ΠΎΡΠ½ΠΎΠ²Π°Π½Π½ΡΡ
Π½Π° ΡΡΠ°Π²Π½Π΅Π½ΠΈΠΈ Π΄ΠΈΡΡΡΠ·ΠΈΠΈ, Π² ΠΊΠΎΡΠΎΡΡΡ
Π² ΠΊΠ°ΡΠ΅ΡΡΠ²Π΅ ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠΎΠ² ΡΠ²Π΅ΡΠ° ΠΈΡΠΏΠΎΠ»ΡΠ·ΡΡΡΡΡ ΡΠΈΠ»ΠΈΠ½Π΄ΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ Π΄ΠΈΡΡΡΠ·ΠΎΡΡ. ΠΠ΅ΡΠ²ΡΠΉ Π°Π»Π³ΠΎΡΠΈΡΠΌ Π°Π½Π°Π»ΠΈΠ·ΠΈΡΡΠ΅Ρ ΡΡΠ°Π²Π½Π΅Π½ΠΈΠ΅ Π΄ΠΈΡΡΡΠ·ΠΈΠΈ ΠΈ ΠΈΠ·ΡΡΠ°Π΅Ρ Π²Π»ΠΈΡΠ½ΠΈΠ΅ ΡΠ°Π·Π»ΠΈΡΠ½ΡΡ
ΠΏΠ΅ΡΠ΅ΠΌΠ΅Π½Π½ΡΡ
(ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ²ΠΎΠΉΡΡΠ² ΠΈΡΡΠΎΡΠ½ΠΈΠΊΠ°, ΠΏΡΠΈΠΌΠ΅Π½ΡΠ΅ΠΌΠΎΠΉ ΠΌΠΎΡΠ½ΠΎΡΡΠΈ, Π΄Π»ΠΈΠ½Ρ Π΄ΠΈΡΡΡΠ·ΠΎΡΠ° ΠΈ Π΅Π³ΠΎ ΠΏΠΎΠ»ΠΎΠΆΠ΅Π½ΠΈΡ). ΠΠ°ΡΠ΅ΠΌ Π±ΡΠ»ΠΈ ΠΈΡΠΏΠΎΠ»ΡΠ·ΠΎΠ²Π°Π½Ρ ΠΏΠ°ΡΠ°ΠΌΠ΅ΡΡΡ ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ²ΠΎΠΉΡΡΠ² ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ Π΄Π»Ρ ΠΎΡΠ΅Π½ΠΊΠΈ ΠΎΠ±ΡΠ΅ΠΌΠ°, ΠΊΠΎΡΠΎΡΡΠΉ ΡΠ°ΡΡΡΠΈΡΡΠ²Π°Π΅Ρ ΡΠ²Π΅ΡΠΎΠ²ΡΡ Π΄ΠΎΠ·Ρ ΠΎΡ ΠΎΠ΄Π½ΠΎΠ³ΠΎ Π΄ΠΈΡΡΡΠ·ΠΎΡΠ°. ΠΠΎ Π²ΡΠΎΡΠΎΠΌ Π°Π»Π³ΠΎΡΠΈΡΠΌΠ΅ Π±ΡΠ»ΠΎ ΡΠΌΠΎΠ΄Π΅Π»ΠΈΡΠΎΠ²Π°Π½ΠΎ Π½Π΅ΡΠΊΠΎΠ»ΡΠΊΠΎ ΡΠ°ΡΡΠ΅ΠΈΠ²Π°ΡΠ΅Π»Π΅ΠΉ Π΄Π»Ρ Π½Π°Ρ
ΠΎΠΆΠ΄Π΅ Π½ΠΈΡ ΡΠΎΠΎΡΠ½ΠΎΡΠ΅Π½ΠΈΡ ΠΌΠ΅ΠΆΠ΄Ρ ΠΎΠ±ΡΠ΅ΠΌΠΎΠΌ ΠΈ ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²ΠΎΠΌ ΡΠ°ΡΡΠ΅ΠΈΠ²Π°ΡΠ΅Π»Π΅ΠΉ, Π½Π΅ΠΎΠ±Ρ
ΠΎΠ΄ΠΈΠΌΡΡ
Π΄Π»Ρ ΠΏΠΎΠΊΡΡΡΠΈΡ ΠΊΡΠ±ΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΈΠ»ΠΈ ΡΠΈΠ»ΠΈΠ½Π΄ΡΠΈΡΠ΅ΡΠΊΠΎΠ³ΠΎ ΠΎΠ±ΡΠ΅ΠΌΠ° Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΠΎΠΉ ΡΠ²Π΅ΡΠΎΠ²ΠΎΠΉ Π΄ΠΎΠ·ΠΎΠΉ. ΠΠ° ΠΏΡΠΎΡΡΠΆΠ΅Π½ΠΈΠΈ Π²ΡΠ΅Π³ΠΎ ΡΡΠΎΠ³ΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΡ ΡΠ°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°Π»ΠΈΡΡ ΡΠ΅Π°Π»ΡΠ½ΡΠ΅ Π·Π½Π°ΡΠ΅Π½ΠΈΡ ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΡ
ΡΠ²ΠΎΠΉΡΡΠ², ΠΊΠ»ΠΈΠ½ΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΌΠΎΡΠ½ΠΎΡΡΠΈ Π»Π°Π·Π΅ΡΠ° ΠΈ Π²ΡΠ΅ΠΌΠ΅Π½ΠΈ Π»Π΅ΡΠ΅Π½ΠΈΡ Π΄Π»Ρ ΠΎΡΠ΅Π½ΠΊΠΈ Π΄ΠΎΡΡΠ°ΡΠΎΡΠ½ΡΡ
ΡΠ²Π΅ΡΠΎΠ²ΡΡ
Π΄ΠΎΠ·. ΠΡΠΎ ΠΈΡΡΠ»Π΅Π΄ΠΎΠ²Π°Π½ΠΈΠ΅ ΡΠΎΠ³Π»Π°ΡΡΠ΅ΡΡΡ Ρ ΠΏΡΠ΅Π΄ΡΠ΄ΡΡΠΈΠΌΠΈ ΡΠ°Π±ΠΎΡΠ°ΠΌΠΈ Π² ΡΠΎΠΌ, ΡΡΠΎ ΠΎΠΏΡΠΈΡΠ΅ΡΠΊΠΈΠ΅ ΡΠ²ΠΎΠΉΡΡΠ²Π° ΡΠ²Π»ΡΡΡΡΡ ΠΎΡΠ½ΠΎΠ²Π½ΡΠΌΠΈ ΡΠ°ΠΊΡΠΎΡΠ°ΠΌΠΈ, Π²Π»ΠΈΡΡΡΠΈΠΌΠΈ Π½Π° ΡΠ°ΡΠΏΡΠ΅Π΄Π΅Π»Π΅Π½ΠΈΠ΅ ΡΠ²Π΅ΡΠ°Β ΠΏΡΠΈ iPDT. ΠΠΎΠΊΠ°Π·Π°Π½ΠΎ, ΡΡΠΎ, Π΄Π»Ρ ΠΎΠ΄Π½ΠΎΡΠΎΠ΄Π½ΠΎΠ³ΠΎ ΡΠ°Π½ΡΠΎΠΌΠ°, ΠΈΠΌΠΈΡΠΈΡΡΡΡΠ΅Π³ΠΎ ΡΠ°ΠΊ ΠΌΠΎΠ»ΠΎΡΠ½ΠΎΠΉ ΠΆΠ΅Π»Π΅Π·Ρ, ΠΊΡΠ±ΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΈΠ»ΠΈ ΡΠΈΠ»ΠΈΠ½Π΄ΡΠΈΡΠ΅ΡΠΊΠΎΠΉ ΡΠΎΡΠΌΡ, ΠΊΠΎΠ»ΠΈΡΠ΅ΡΡΠ²ΠΎ ΡΡΠ΅Π±ΡΠ΅ΠΌΡΡ
Π²ΠΎΠ»ΠΎΠΊΠΎΠ½ N ΡΠ°Π²Π½ΠΎ WΓL ΠΈΠ»ΠΈ D2 , ΡΠΎΠΎΡΠ²Π΅ΡΡΡΠ²Π΅Π½Π½ΠΎ
Cotunneling drag effect in Coulomb-coupled quantum dots
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
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
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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