Simple is beautiful in quantum computing

November 15, 2017, US Department of Energy
Simple is beautiful in quantum computing
Quantum computers use electron spin orientation at a defect site in diamond to store information. The electron spin can be up (+1), down (-1), or anything in between. The spin (left, red arrow) is represented as a vector on a sphere. To change the spin from Position 1 to 2 normally requires two separate optical pulses. However, here a particular single pulse has accomplished the same electronic transition. This single pulse makes the electron travel on a geometric loop, analogous to a Möbius strip (right, a surface with one side and one boundary), such that its position is changed in a robust way after completing the loop. Credit: US Department of Energy

Quantum computing could solve problems impossible for today's supercomputers. The challenge for this new form of computing is processing the quantum bits (qubits) that represent data. A qubit can be made by controlling the orientation of an electron's spin at a defect site in diamond. To solve a problem, a quantum computer uses logic gates to couple multiple qubits and output new information. Scientists designed a new protocol that can be used to develop fast, robust logic gates for qubits. The simple gates reorient electron spin on defect sites in diamond. This new finding would allow faster and more efficient manipulation of the electron spins or qubits.

Researchers exert a new form of fast geometric control on the electron's spin orientation. This enables faster and fewer gates to achieve the same operation on the qubit as conventional techniques, thus facilitating the development of future quantum computers. As an added bonus, the new gates are also less sensitive to noise than today's operations (specifically, sequential, multi-pulse operations). Noise can destroy quantum information. Controlling qubits has the potential to bring us closer to practical quantum computers. It could advance our ability to develop high fidelity quantum logic.

Classical computers are number crunching machines, performing basic arithmetical operations on numbers. In computer language, these numbers are expressed in binary number units of zeros and ones, also called bits. Each bit, therefore, stores the smallest piece of information and can accept a value of either 1 or 0. Similar to classical computers, quantum computers are designed to operate on . An extraordinary property of qubits is that they can be of any value equal to or between -1 and +1, until we measure them. As in a classical computer, the initial states of qubits need to be prepared before quantum data processing or data storage.

Diamond is a very promising material for . In diamond, a nitrogen atom can replace a carbon atom. When the nitrogen is next to a missing carbon atom in the crystalline lattice, this is called a nitrogen-vacancy defect. As well as possessing charge, this impurity possesses a property known as spin that can be used to store . Its spin can be initialized, manipulated, and "read out" with a laser at room temperature, unlike other architectures that require low temperatures. This single impurity can emit one photon at a time. A photon can carry one qubit of information. Researchers discovered a simple method to prepare and manipulate the quantum state of a nitrogen-vacancy center acting as a . Gates are used to prepare and manipulate the electronic transitions of qubits. A geometric gate relies on the evolution or geometric path of the spin instead of energy differences involved in the used in traditional computers. This particular geometric gate utilizes a single laser pulse to send the through a high-speed cycle. The geometry of the cycle is controlled by the single laser pulse and determines the final gate operations and electronic transitions. Further, careful control of the pulse energy significantly improved the fidelity of the electronic transition compared to traditional multi-pulse techniques, simplifying the path to practical technologies.

Explore further: Quantum computing on the move

More information: Brian B. Zhou et al. Holonomic Quantum Control by Coherent Optical Excitation in Diamond, Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.140503

Related Stories

Quantum computing on the move

November 7, 2017

A future quantum computer, using quantum bits, or qubits, might be able to solve problems that are not tractable for classical computers. Scientists are currently struggling to build devices with more than a few qubits, as ...

A new kind of quantum computer

November 6, 2017

Quantum mechanics incorporates some very non-intuitive properties of matter. Quantum superposition, for example, allows an atom to be simultaneously in two different states with its spin axis pointed both up and down, or ...

Quantum computing building blocks

July 24, 2017

For decades scientists have known that a quantum computer—a device that stores and manipulates information in quantum objects such as atoms or photons—could theoretically perform certain calculations far faster than today's ...

Stable quantum bits can be made from complex molecules

November 10, 2016

Quantum computing is about to get more complex. Researchers have evidence that large molecules made of nickel and chromium can store and process information in the same way bytes do for digital computers. The researchers ...

How quantum mechanics can change computing

August 24, 2017

In early July, Google announced that it will expand its commercially available cloud computing services to include quantum computing. A similar service has been available from IBM since May. These aren't services most regular ...

Recommended for you

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

milnik
not rated yet Dec 22, 2017
The electrons circle around the nucleus of the atom and possess their spin, which depends on the kinetic energy of the radial velocity, in relation to the energy or center of the mass of the electron. Photon motion is more complicated because the photon energy state is formed when the radius of electron motion changes and, with the participation of Aether, a "condensate" of an electron-positron pair obtained from Aether is formed. This "aether positron" moves straight-line with its spin, and "aether-electron" rotates around "ap" by a sinusoidal radius around the center of their energy state. Thus, this pair is impossible to hold in a "cage" and take it from it to quantum state . Only spin of the electron should be used here without changing the energy level.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.