Info
Info
News Article

Scientists Create Identical Quantum Dots And Place Them With Pinpoint Precision

Research opens the door to quantum dot architectures completely free of uncontrolled variations

The ambitious goal of creating quantum dots with digital fidelity by eliminating variations in their size, shape and arrangement has remained elusive. Such perfect reproducibility is important as it opens the door to quantum dot architectures  free of uncontrolled variations, which is necessary for technologies ranging from nanophotonics to quantum information processing.

Now scientists from Paul-Drude-Institute for Solid-State Physics in Berlin, NTT Basic Research Laboratories, Japan; and the Naval Research Laboratory (NRL), USA have managed to create quantum dots with identical, deterministic sizes, according to a recent report in Nature Nanotechnology.

Quantum dots are often called artificial atoms because, like real atoms, they confine electrons to quantised states with discrete energies. But real atoms are identical, whereas most quantum dots comprise hundreds or thousands of atoms, with variations in size and shape and, consequently, unavoidable variability in their wavefunctions and energies.

Creating atomically precise quantum dots requires every atom of the quantum dot to be placed in a precisely specified location without error, and multiple dots to be arranged in exactly defined configurations without variation. The researchers achieved this goal using a scanning tunnelling microscope (STM) to manipulate the atoms and an atomically precise surface template to define a lattice of allowed atomic 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. 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.

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 say they have created degenerate states that are surprisingly resistant to environmental perturbations by defects. 

The reproducibility and high fidelity offered by these quantum dots makes them excellent candidates for studying fundamental physics. 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 technologies from nanophotonics to quantum information processing.

Figures a,b, c and d above show the quantized states of a digital quantum dot in which electrons are confined by a chain of ionized indium adatoms. Picture a, is a topographic STM image (0.1 nA, _0.3 V) of a chain of indium adatoms assembled on InAs(111)A. Twenty-two indium atoms were placed on adjacent indium-vacancy sites of the (2 x 2)-reconstructed surface. b, shows the atomic structure of the image section indicated in a. The surface consists of indium (green) and arsenic (orange) atoms, and the chain is formed by In adatoms (black circles) adsorbed above vacancy sites. c, shows the differential conductance (dI/dV) spectra (red and blue) recorded at the off-chain tip positions indicated in a, revealing quantized electron states with quantum numbers n = 1-7. The reference spectrum of pristine InAs(111)A (green) reveals that the Fermi level is pinned in the conduction band due to intrinsic electron accumulation at the surface. d, Spatial DOS maps D(x,y) obtained by constant-height dI/dV scanning at the bias voltages corresponding to the resonances in c. Quantized states for n = 1-6, each with n lobes and n- 1 nodes, are clearly revealed.

This work is described in Nature Nanotechnology 9, 505-508 (2014)  'Quantum dots with single-atom precision' by Stefan Folsch et al.

doi:10.1038/nnano.2014.129



AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.

REGISTER FOR FREE

VIEW SESSIONS

Info
×
Search the news archive

To close this popup you can press escape or click the close icon.
×
Logo
×
Register - Step 1

You may choose to subscribe to the Compound Semiconductor Magazine, the Compound Semiconductor Newsletter, or both. You may also request additional information if required, before submitting your application.


Please subscribe me to:

 

You chose the industry type of "Other"

Please enter the industry that you work in:
Please enter the industry that you work in:
 
X
Info
X
Info
{taasPodcastNotification}
Live Event