Quantum
Computing- II Which technology to choose? |
||
26th
November 2017 |
||
"The quantum phenomena does not
occur in Hilbert space. They occur in a
laboratory."
- Asher Peres. "Topological quantum computation", Sankar Das Sarma et. al., Physics Today, July 2006. "As you will see, the entry fee is pretty steep, which provides at least one good reason why all sorts of people aren’t already putting together their quantum processors." - D. P. Divincenzo |
The limitations of the
existing digital technology in performing quantum
computations were discussed earlier. It
was clear that we had to think beyond the
traditional silicon based technologies which were
used in a wide range of computational
devices. So
the immediate problem now became, how to define
the criterion for the technology considered
suitable for quantum computing. In other words, the physical bits storing information about Qubits, must not have any interaction among themselves due to external environmental factors, before the measurement on the final state of the Quantum Computer is made. It is estimated that at the room temperature (300 K) and macroscopic scales, the quantum coherence is destroyed in 10-23 seconds. This is the problem of "decoherence" affecting the realization of the quantum computing. In a carefully controlled laboratory environment, (ultra-low temperature, ultra-high vacuum and magnetic shielding), the decoherence time can be improved at the atomic scale. Please note by mentioning atomic scale we are moving away from conventional digital technology as we know it. The decoherence time for a Qubit in a quantum computer, is characterized by the following parameters1:
Ion-traps provide
highest CQF, but building a system with large
number of Qubits is a problem. Photonic
qubits (Cavity-QED Optical) have similar issues
related to the scalability despite high
CQF. NMR based system has limited
scalability as number of states which can be
stored on each molecule, themselves are limited.
The SQUID (Superconducting Quantum Interference Devices) technology, is currently used by IBM and D-Wave. SQUID has the advantage that it uses most of the techniques and equipment available in microelectronics manufacturing. Hence there is smaller learning curve and the end-product is reliable. The drawback is low CQF and therefore stringent environmental controls are required. Quantum dots are based on the principle that if the electron gas is confined in 3-D within Fermi length (~nm) in a perfect lattice configuration in compound semiconductors, its energy levels are quantized. The real advantage is that by changing the location of atoms in the lattice, the energy levels can be precisely fine-tuned. If the technology can be improved to increase CQF values for quantum dots, they can provide an effective solution within the existing solid-state technology. The technologies discussed so far, have their limitations as far as the true quantum computing is concerned. They provide probabilistic solutions, i.e. the same problem is run multiple times to get multiple answers which are within a certain range. We then pick the most probable solution. However this is still a high entropy procedure as we have to make multiple measurements to get the most probable solution. Ideally we want a single measurement, a zero-entropy procedure and a deterministic solution. How to accomplish this rather idiosyncratic objective? To do so we must move beyond relativistic limits and eliminate the time-axis completely. We will be discussing some topological concepts in j-space next. ______________
1. Quantum Computing
Devices: Principles, Designs and Analysis
by Goong Chen, David A. Church,
Berthold-Georg Englert, Carsten Henkel, Bernd
Rohwedder, Marlan O. Scully, and M. Suhail
Zubairy.
|
Previous Blogs:
Quantum Computing
- I
Insincere Symmetry - II Insincere Symmetry - I 3-D Infinite Source Nutshell-2016 Quanta-II Quanta-I EPR Paradox-II Chiral Symmetry
Sigma-z and I Spin Matrices Rationale behind Irrational Numbers The Ubiquitous z-Axis Majorana ZFC Axioms Set Theory Nutshell-2014 Knots in j-Space Supercolliders Force Riemann Hypothesis Andromeda Nebula Infinite Fulcrum Cauchy and Gaussian Distributions Discrete Space, b-Field & Lower Mass Bound Incompleteness II The Supersymmetry The Cat in Box The Initial State and Symmetries Incompleteness I Discrete Measurement Space The Frog in Well Visual Complex Analysis The Einstein Theory of Relativity |
Best viewed with
Internet Explorer
Information on www.ijspace.org is licensed under a Creative Commons Attribution 4.0 International License.