Single Atom Quantum Computing in Silicon
Δημοσιεύτηκε στις 15 Ιουν 2013
Using
existing Silicon fabrication facilities, it is possible to dope a high
purity silicon chip with a single phosphorus donor atom and manipulate
the atom using a varying magnetic field to manipulate the quantum spin
state of the atom to form a quantum bit or qubit.
The nucleus of
the phosphorus atom can store a single qubit for long periods of time
in the way it spins. A magnetic field could easily address this qubit
using well-known techniques from nuclear magnetic resonance
spectroscopy. This allows single-qubit manipulations but not two-qubit
operations, because nuclear spins do not interact significantly of each
other.
For that, we must transfer the spin quantum number of the
nucleus to an electron orbiting the phosphorus atom, which would
interact much more easily with an electron orbiting a nearby phosphorus
atom. Two-qubit operations would then be possible by manipulating the
two electrons with high frequency AC electric fields.
The big
advantage of this type of quantum computer, sometimes called the Kane
quantum computer after physicist Bruce Kane who suggested the device
back in the late 1990's, is that it is scalable. Since each atom could
be addressed individually using standard electronic circuitry, it is
straightforward to increase the size of the computer by adding more
atoms and their associated electronics and then to connect it to a
conventional computer.
The disadvantages of course is that the
atoms must be placed at precise locations in the Silicon, using a
scanning tunneling microscope. The manipulation of the phosphorus atom
spin itself is also problematic as this requires powerful magnetic
fields which reduces scalability.
But the big unsolved challenge
has been to find a way to address the spin of an individual electron
orbiting a phosphorus atom and to read out its value.
To do this
requires scientists to implant a single phosphorus atom in a silicon
nanostructure and place it in a powerful magnetic field at a temperature
close to absolute zero, cooling the chip using liquid helium. This
makes it possible to flip the state of an electron orbiting the
phosphorus atom by irradiating it with microwaves.
The final
step, a significant challenge in itself, is to read out the state of the
electron using a process known as spin-to-charge conversion.
The
end result is a device that can store and manipulate a qubit and has
the potential to perform two-qubit logic operations with atoms nearby;
in other words the fundamental building block of a scalable quantum
computer.
However, some stiff competition has emerged in the 15 years since Kane published his original design.
In
particular, physicists have found a straightforward way to store and
process quantum information in nitrogen vacancy defects in diamond,
which offer the best possibility to make a functional quantum computer
as this structure can produced quantum gate operations that can work at
room temperature.
Then there is D-Wave Systems, which already
manufactures a scalable quantum computer working in an entirely
different way that it has famously sold to companies such as Lockheed
Martin and Google.
The big advantage of the Australian design is
its compatibility with the existing silicon-based chip-making industry.
In theory, it will be straightforward to incorporate this technology
into future chips.
Currently, the Australian Kane quantum computer has the highest performance capabilities of any solid state qubit.
Due
to the ease of reproducing the diamond NV- centers, their ease of
operation without using liquid helium to cool the chip as well as their
speed using optics and electronics it seems that diamond based quantum
computers are providing the biggest competition to the Kane quantum
computer in the race to develop a functioning, gate quantum computer.
Ref: arxiv.org/abs/1305.4481: A single-Atom Electron Spin Qubit in Silicon
existing Silicon fabrication facilities, it is possible to dope a high
purity silicon chip with a single phosphorus donor atom and manipulate
the atom using a varying magnetic field to manipulate the quantum spin
state of the atom to form a quantum bit or qubit.
The nucleus of
the phosphorus atom can store a single qubit for long periods of time
in the way it spins. A magnetic field could easily address this qubit
using well-known techniques from nuclear magnetic resonance
spectroscopy. This allows single-qubit manipulations but not two-qubit
operations, because nuclear spins do not interact significantly of each
other.
For that, we must transfer the spin quantum number of the
nucleus to an electron orbiting the phosphorus atom, which would
interact much more easily with an electron orbiting a nearby phosphorus
atom. Two-qubit operations would then be possible by manipulating the
two electrons with high frequency AC electric fields.
The big
advantage of this type of quantum computer, sometimes called the Kane
quantum computer after physicist Bruce Kane who suggested the device
back in the late 1990's, is that it is scalable. Since each atom could
be addressed individually using standard electronic circuitry, it is
straightforward to increase the size of the computer by adding more
atoms and their associated electronics and then to connect it to a
conventional computer.
The disadvantages of course is that the
atoms must be placed at precise locations in the Silicon, using a
scanning tunneling microscope. The manipulation of the phosphorus atom
spin itself is also problematic as this requires powerful magnetic
fields which reduces scalability.
But the big unsolved challenge
has been to find a way to address the spin of an individual electron
orbiting a phosphorus atom and to read out its value.
To do this
requires scientists to implant a single phosphorus atom in a silicon
nanostructure and place it in a powerful magnetic field at a temperature
close to absolute zero, cooling the chip using liquid helium. This
makes it possible to flip the state of an electron orbiting the
phosphorus atom by irradiating it with microwaves.
The final
step, a significant challenge in itself, is to read out the state of the
electron using a process known as spin-to-charge conversion.
The
end result is a device that can store and manipulate a qubit and has
the potential to perform two-qubit logic operations with atoms nearby;
in other words the fundamental building block of a scalable quantum
computer.
However, some stiff competition has emerged in the 15 years since Kane published his original design.
In
particular, physicists have found a straightforward way to store and
process quantum information in nitrogen vacancy defects in diamond,
which offer the best possibility to make a functional quantum computer
as this structure can produced quantum gate operations that can work at
room temperature.
Then there is D-Wave Systems, which already
manufactures a scalable quantum computer working in an entirely
different way that it has famously sold to companies such as Lockheed
Martin and Google.
The big advantage of the Australian design is
its compatibility with the existing silicon-based chip-making industry.
In theory, it will be straightforward to incorporate this technology
into future chips.
Currently, the Australian Kane quantum computer has the highest performance capabilities of any solid state qubit.
Due
to the ease of reproducing the diamond NV- centers, their ease of
operation without using liquid helium to cool the chip as well as their
speed using optics and electronics it seems that diamond based quantum
computers are providing the biggest competition to the Kane quantum
computer in the race to develop a functioning, gate quantum computer.
Ref: arxiv.org/abs/1305.4481: A single-Atom Electron Spin Qubit in Silicon
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