Featured Research

from universities, journals, and other organizations

Quantum dots created with single-atom precision

Date:
June 30, 2014
Source:
Forschungsverbund Berlin e.V. (FVB)
Summary:
Physicists have used a scanning tunneling microscope to create quantum dots with identical, deterministic sizes. The perfect reproducibility of these dots opens the door to quantum dot architectures completely free of uncontrolled variations, an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies.

Quantized electron states, for quantum numbers n = 1 to 6, of a linear quantum dot consisting of 22 indium atoms positioned on the surface of an InAs crystal.
Credit: PDI

A team of physicists from the Paul-Drude-Institut für Festkörperelektronik (PDI) in Berlin, Germany, NTT Basic Research Laboratories (NTT-BRL) in Atsugi, Japan, and the U.S. Naval Research Laboratory (NRL) has used a scanning tunneling microscope to create quantum dots with identical, deterministic sizes. The perfect reproducibility of these dots opens the door to quantum dot architectures completely free of uncontrolled variations, an important goal for technologies from nanophotonics to quantum information processing as well as for fundamental studies. The complete findings are published in the July 2014 issue of the journal Nature Nanotechnology.

Related Articles


Quantum dots are often regarded as artificial atoms because, like real atoms, they confine their electrons to quantized states with discrete energies. But the analogy breaks down quickly, because while real atoms are identical, quantum dots usually comprise hundreds or thousands of atoms -- with unavoidable variations in their size and shape and, consequently, in their properties and behavior. External electrostatic gates can be used to reduce these variations. But the more ambitious goal of creating quantum dots with intrinsically perfect fidelity by completely eliminating statistical variations in their size, shape, and arrangement has long remained elusive.

Creating atomically precise quantum dots requires every atom to be placed in a precisely specified location without error. The team assembled the dots atom-by-atom, using a scanning tunneling microscope (STM), and relied on an atomically precise surface template to define a lattice of allowed atom positions. The template was the surface of an InAs crystal, which has a regular pattern of indium vacancies and a low concentration of native indium adatoms adsorbed above the vacancy sites. Kiyoshi Kanisawa, a physicist at NTT-BRL and the team's expect in crystal growth, used the technique of molecular beam epitaxy to fabricate this InAs surface. The adatoms are ionized +1 donors and can be moved with the STM tip by vertical atom manipulation. The team assembled quantum dots consisting of linear chains of N = 6 to 25 indium atoms; the exampleshown here is a chain of 22 atoms.

Stefan Fölsch, a physicist at the PDI who led the team, explained that "the ionized indium adatoms form a quantum dot by creating an electrostatic well that confines electrons normally associated with a surface state of the InAs crystal. The quantized states can then be probed and mapped by scanning tunneling spectroscopy measurements of the differential conductance." These spectra show a series of resonances labeled by the principal quantum number n. Spatial maps reveal the wave functions of these quantized states, which have n lobes and n - 1 nodes along the chain, exactly as expected for a quantum-mechanical electron in a box. For the 22-atom chain example, the states up to n = 6 are shown.

Because the indium atoms are strictly confined to the regular lattice of vacancy sites, every quantum dot with N atoms is essentially identical, with no intrinsic variation in size, shape, or position. This means that quantum dot "molecules" consisting of several coupled chains will reflect the same invariance. Steve Erwin, a physicist at NRL and the team's theorist, pointed out that "this greatly simplifies the task of creating, protecting, and controlling degenerate states in quantum dot molecules, which is an important prerequisite for many technologies." In quantum computing, for example, qubits with doubly degenerate ground states offer protection against environmental decoherence. By combining the invariance of quantum dot molecules with the intrinsic symmetry of the InAs vacancy lattice, the team created degenerate states that are surprisingly resistant to environmental perturbations by defects. In the example shown here, a molecule with perfect three-fold rotational symmetry was first created and its two-fold degenerate state demonstrated experimentally. By intentionally breaking the symmetry, the team found that the degeneracy was progressively removed, completing the demonstration.

The reproducibility and high fidelity offered by these quantum dots makes them excellent candidates for studying fundamental physics that is typically obscured by stochastic variations in size, shape, or position of the chains. Looking forward, the team also anticipates that the elimination of uncontrolled variations in quantum dot architectures will offer many benefits to a broad range of future quantum dot technologiesin which fidelity is important.


Story Source:

The above story is based on materials provided by Forschungsverbund Berlin e.V. (FVB). Note: Materials may be edited for content and length.


Journal Reference:

  1. Stefan Fölsch, Jesús Martínez-Blanco, Jianshu Yang, Kiyoshi Kanisawa, Steven C. Erwin. Quantum dots with single-atom precision. Nature Nanotechnology, 2014; DOI: 10.1038/NNANO.2014.129

Cite This Page:

Forschungsverbund Berlin e.V. (FVB). "Quantum dots created with single-atom precision." ScienceDaily. ScienceDaily, 30 June 2014. <www.sciencedaily.com/releases/2014/06/140630094535.htm>.
Forschungsverbund Berlin e.V. (FVB). (2014, June 30). Quantum dots created with single-atom precision. ScienceDaily. Retrieved November 23, 2014 from www.sciencedaily.com/releases/2014/06/140630094535.htm
Forschungsverbund Berlin e.V. (FVB). "Quantum dots created with single-atom precision." ScienceDaily. www.sciencedaily.com/releases/2014/06/140630094535.htm (accessed November 23, 2014).

Share This


More From ScienceDaily



More Matter & Energy News

Sunday, November 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

Toyota's Hydrogen Fuel-Cell Green Car Soon Available in the US

AFP (Nov. 21, 2014) — Toyota presented its hydrogen fuel-cell compact car called "Mirai" to US consumers at the Los Angeles auto show. The car should go on sale in 2015 for around $60.000. It combines stored hydrogen with oxygen to generate its own power. Duration: 01:18 Video provided by AFP
Powered by NewsLook.com
Google Announces Improvements To Balloon-Borne Wi-Fi Project

Google Announces Improvements To Balloon-Borne Wi-Fi Project

Newsy (Nov. 21, 2014) — In a blog post, Google said its balloons have traveled 3 million kilometers since the start of Project Loon. Video provided by Newsy
Powered by NewsLook.com
Raw: Paralyzed Marine Walks With Robotic Braces

Raw: Paralyzed Marine Walks With Robotic Braces

AP (Nov. 21, 2014) — Marine Corps officials say a special operations officer left paralyzed by a sniper's bullet in Afghanistan walked using robotic leg braces in a ceremony to award him a Bronze Star. (Nov. 21) Video provided by AP
Powered by NewsLook.com
British 'Bio-Bus' Is Powered By Human Waste

British 'Bio-Bus' Is Powered By Human Waste

Buzz60 (Nov. 21, 2014) — British company GENeco debuted what its calling the Bio-Bus, a bus fueled entirely by biomethane gas produced from food scraps and sewage. Jen Markham explains. Video provided by Buzz60
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins