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EP-4740145-A1 - A METHOD FOR DETERMINING VALLEY-SPLITTING IN A SEMICONDUCTOR DEVICE

EP4740145A1EP 4740145 A1EP4740145 A1EP 4740145A1EP-4740145-A1

Abstract

A method of determining a valley splitting of a semiconductor device comprises setting a field strength of an external magnetic field B, for splitting entangled spin states associated with a double quantum dot generated in the semiconductor device; evolving the entangled spin states for an evolution period; measuring a state of the entangled spin states in a basis of the entangled spin states, the basis comprising at least two basis states; repeating the evolving and the measuring to determine a probability of the state of the entangled spin states being at least one of the at least two basis states; and assessing, based on the determined probability, the valley splitting.

Inventors

  • SCHREIBER, Lars Reiner
  • STRUCK, Tom
  • VOLMER, Mats
  • BLUHM, Jörg Hendrik

Assignees

  • Rheinisch-Westfälische Technische Hochschule (RWTH) Aachen
  • Forschungszentrum Jülich GmbH

Dates

Publication Date
20260513
Application Date
20230929

Claims (12)

  1. 1. A method of determining a valley splitting of a semiconductor device (10,11), the method comprising - setting (100) a field strength of an external magnetic field B for splitting entangled spin states associated with a double quantum dot (QDl,QDm) generated in the semiconductor device (10, 11); - evolving (400) the entangled spin states for an evolution period (TA); - measuring (700) a state of the entangled spin states in a basis of the entangled spin states, the basis comprising at least two basis states; - repeating (800) the evolving (400) and the measuring (700) to determine a probability of the state of the entangled spin states being one of the at least two basis states; and - assessing, based on the determined probability, the valley splitting.
  2. 2. The method of claim 1, wherein the entangled spin states are associated with a first electron or hole and a second electron or hole, arranged in the double quantum dot (QD1, QDm).
  3. 3. The method of claim 1 or 2, further comprising arranging (160) the double quantum dot (QD1, QDm) at a lateral position (y) of the semiconductor device (10).
  4. 4. The method of any one of claims 1 to 3, further comprising moving (300, 500) at least one moveable quantum dot (QDm) of the double quantum dot (QD1, QDm) by a distance d along at least one shuttling path (45) of the semiconductor device (10).
  5. 5. The method of claim 4, wherein the moving (300) is performed before the evolving (400) of the entangled spin states.
  6. 6. The method of claim 4 or 5, wherein the moving (500) is performed after the evolving (400) of the entangled spin states.
  7. 7. The method of any one of claims 1 to 6, wherein the repeating (800) comprises maintaining the shuttling distance d or altering the shuttling distance d.
  8. 8. The method of any one of claims 1 to 7, wherein the repeating (800) comprises maintaining the field strength of the external magnetic field B or altering the field strength of the external magnetic field B.
  9. 9. The method of any one of claims 1 to 8, further comprising initialising (200) a first quantum state of the first electron or hole, and initialising (200) a second quantum state of the second electron or hole.
  10. 10. The method of any one of claims 1 to 9, further comprising measuring (700) the occupancy state of the loadable quantum dot (QD1).
  11. 11. The method of any one of claims 1 to 10, further comprising loading (180) the first electron or hole and the second electron or hole in the double quantum dot (QD1, QDm).
  12. 12. The method of any one of claims 1 to 11, further comprising identifying (900) a valley splitting by detecting anomalous behaviour the oscillations of the entangled spin states between the two basis states.

Description

Description Title: A method for determining valley-splitting in a semiconductor device [0001] The present invention relates to a method for determining valley-splitting in a semiconductor heterostructure. Background of the invention [0002] Silicon is semiconductor used extensively in current micro- and nanoelectronics. Silicon has enabled the semiconductor industry to meet Moore’s law during the last few decades. Nowadays, billions of nanometre-scale transistors per chip are being manufactured. [0003] Silicon is also a promising candidate for quantum computing based on qubits encoded in spins (spin states) of electrons confined in quantum dots. Recent advances show that a two-dimensional architecture based on a silicon heterostructure and structured electrode gates for quantum computing with several qubits is in reach (see Matthias Kiinne et al. arXiv: 2306.16348 (2023)). [0004] In order to make such silicon-based quantum computing possible, however, a degeneracy involving six conduction band minima (valleys) in a silicon structure, including a silicon heterostructure, must be overcome. One way of lifting the degeneracy is by straining the crystal lattice of the silicon structure (e.g., by depositing a layer of silicon onto a silicon germanium (SiGe) substrate) or by exposing the silicon structure to an electrical field. The strain or the exposure to the electrical field can reduce or eliminate the valley degeneracy by bringing the degenerate valleys to different energy levels. The energy difference between a ground state of one valley and the next higher valley is often referred to as valley splitting (Evs). [0005] One disadvantage of straining, and/or exposing to electrical fields of the silicon structure is that electron mass and electron mobility are affected, which impacts on the functioning of the silicon structure with dimensions in the nano-range. [0006] However, valley splitting that is sufficiently large enables the generation of well- defined (i.e., unlikely to transition to other quantum states) and long-lived (i.e., with sufficiently long decoherence times to enable qubit operations) spin-qubits in the silicon structure. [0007] Moreover, for valley-qubits in silicon based on two of the six valleys, the valley splitting has to be known. For hybrid qubits, e.g., hybrid of a spin-qubit and a charge-qubit, the valley splitting has to be both known and adjustable. [0008] For quantum processor architectures based on the shuttling of spin-qubits (see Matthias Kiinne et al. arXiv: 2306.16348 (2023)), the valley splitting has to be sufficiently large in order to enable coherent shuttling of the spin-qubits. As the valley splitting depends on local properties (local strain, local electrical fields, atomic details) of the silicon structure, a two-dimensional determination of the valley splitting across the silicon structure is desirable. Summary of the disclosure [0009] The present disclosure relates to method for determining valley-splitting of a semiconductor heterostructure. [0010] A method of determining a valley splitting of a semiconductor device comprises setting a field strength of an external magnetic field B, for splitting entangled spin states associated with a double quantum dot generated in the semiconductor device; evolving the entangled spin states for an evolution period; measuring a state of the entangled spin states in a basis of the entangled spin states, the basis comprising at least two basis states; repeating the evolving and the measuring to determine a probability of the state of the entangled spin states being at least one of the at least two basis states; and assessing, based on the determined probability, the valley splitting. [0011] The entangled spin states may be associated with a first electron or hole and a second electron or hole, arranged in the double quantum dot. [0012] The method may further comprise arranging the double quantum dot at a lateral position of the semiconductor device. [0013] The method may further comprise moving at least one moveable quantum dot of the double quantum dot by a distance d along at least one shuttling path of the semiconductor device. [0014] The moving may be performed before the evolving of the entangled spin states. [0015] The moving may be performed after the evolving of the entangled spin states. [0016] The repeating may comprise maintaining the shuttling distance d or altering the shuttling distance d. [0017] The repeating may comprise maintaining the field strength of the external magnetic field B or altering the field strength of the external magnetic field B. [0018] The method may further comprise initialising a first quantum state of the first electron or hole, and initialising a second quantum state of the second electron or hole. [0019] The method may further comprise measuring the occupancy state of the loadable quantum dot. [0020] The method may further comprise loading the first electron or hole and the second electron or