• Physics 18, s110
Experiments show that one of the standard electrode types for semiconductor-based quantum processors isn’t needed.
Tapping into computer-chip technology is one of the advantages to building a quantum computer using quantum bits (qubits) hosted by semiconductor quantum dots—tiny “islands” of charge that can be manipulated with electrodes. But one challenge for scaling up to large qubit numbers is the number of individual electrodes required. Now Alexander Ivlev of the Delft University of Technology in the Netherlands and his colleagues have shown a way to dispense with barrier gates—a type of electrode that was thought to be needed to connect every neighboring pair of quantum dots [1]. The researchers say that using this new approach could increase the numbers of qubits on a chip and thus improve the usefulness of solid-state quantum processors.
In a two-qubit operation, the qubits can be thought of as quantum particles inhabiting potential wells separated by a barrier. Controlling this barrier’s height is key to the operation, and in the usual design, the height is set by the voltage applied to a barrier gate that sits between two quantum dots. The chip needs one of these independently controlled barrier gates for every pair of neighboring quantum dots, and it also needs a so-called plunger gate for each quantum dot in order to control the depth of every qubit’s potential well.
Ivlev and colleagues showed that they could perform two-qubit operations without needing to control a barrier gate. Instead of changing the barrier height directly, they achieved a similar effect by using the plunger gates to change the relative depths of the wells. The researchers also showed that their scheme does not significantly reduce qubit coherence, an essential property for quantum information processing.
–David Ehrenstein
David Ehrenstein is a Senior Editor for Physics Magazine.
References
- A. S. Ivlev, “Operating semiconductor qubits without individual barrier gates,” Phys. Rev. X 15, 031042 (2025).
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