Search

EP-4740146-A1 - QUBIT INITIALISATION METHOD AND DEVICE

EP4740146A1EP 4740146 A1EP4740146 A1EP 4740146A1EP-4740146-A1

Abstract

A method for qubit initialisation comprising the steps of: (i) setting a two-qubit state of a pair of spin qubits to any state; (ii) verifying a qubit state associated with the pair of spin qubits against a corresponding target state; and (iii) in response to determining, at step (ii), that the qubit state is not the target state, repeating steps (i) to (ii) until the qubit state is determined as the target state. Determining the qubit state as the target state includes performing one or more Pauli-spin blockade (PSB) checks, and at least one two-qubit state conversion operation, on the pair of spin qubits.

Inventors

  • Saraiva de Oliveira, André Luiz
  • YANG, Chih-Hwan Henry
  • HUANG, Jonathan Yue

Assignees

  • Diraq Pty Ltd

Dates

Publication Date
20260513
Application Date
20240703

Claims (20)

  1. CLAIMS: 1. A method for qubit initialisation, comprising: (i) setting a two-qubit state of a pair of spin qubits to any state; (ii) verifying a qubit state associated with the pair of spin qubits against a corresponding target state; and (iii) in response to determining, at step (ii), that the qubit state is not the target state, repeating steps (i) to (ii) until the qubit state is determined as the target state, wherein determining the qubit state as the target state includes performing one or more Pauli-spin blockade (PSB) checks and at least one two-qubit state conversion operation, on the pair of spin qubits.
  2. 2. The method of claim 1, wherein the two-qubit state is reset by performing step (i) in response to one of the one or more PSB checks determining that the two-qubit state is unblockaded.
  3. 3. The method of claim 2, wherein each of the PSB checks comprises performing a readout operation on the spin qubits of the pair within a PSB lifetime to maintain the two-qubit state in response to the two-qubit state being a blockaded state.
  4. 4. The method of any of claims 1 to 3, wherein the qubit state associated with the pair of spin qubits is a single-qubit state of one of the spin qubits of the pair.
  5. 5. The method of any of claims 1 to 3, wherein the qubit state associated with the pair of spin qubits is the two-qubit state and the target state is a blockaded state.
  6. 6. The method of claim 5, wherein each two-qubit state conversion operation includes a two-qubit gate configured to convert the two-qubit state to an unblockaded state, in response to the two-qubit state being a blockaded state and a different state to the target state.
  7. 7. The method of claim 6, of the PSB checks is a parity PSB check performed over two-qubit basis states of |↓↓^, |↓↑^, |↑↓^, and |↑↑^.
  8. 8. The method of claim 7, wherein the target state is an even spin parity state, being one of the |↑↑^ and |↓↓^ states, and wherein the two-qubit gate converts the other of the even states |↑↑^ and |↓↓^ into an odd parity state, being one of the |↑↓^ and |↓↑^ states.
  9. 9. The method of claim 8, wherein the target state is |↓↓^ and the two-qubit gate is a zero-control-not gate (zCNOT) configured to convert |↑↑^ into |↑↓^.
  10. 10. The method of claim 9, wherein the two-qubit state is determined to be: an even parity state, being one of |↓↓^ and |↑↑^, if a first PSB check indicates a blockade; or an odd parity state, being one of |↓↑^ and |↑↓^, if the first PSB check indicates the absence of a blockade.
  11. 11. The method of claim 10, wherein the two-qubit state is determined to be: even parity state |↓↓^ if a second PSB check indicates a blockade; or odd parity state |↑↓^ if the second PSB check indicates the absence of a blockade.
  12. 12. The method of claim 6, wherein each of the PSB checks is a singlet-triplet (ST) PSB check performed over two-qubit basis states of |↓↓^, |S^, |T 0 ^, and |↑↑^, where states |S^ and |T 0 ^ are the singlet and triplet states respectively.
  13. 13. The method of claim 12, wherein determining the two-qubit state as the target state includes performing: a first PSB check, one or more single-qubit rotations on the spin qubits to convert |T 0 ^ into |S^, a second PSB check, a two-qubit gate, and a third PSB check, on the pair of spin qubits.
  14. 14. The method of claim 13, wherein the target state is |↓↓^ and the two-qubit gate is a zero-control-not gate (zCNOT) configured to convert |↑↑^ into |S^.
  15. 15. The method of claim 14, wherein the two-qubit state is determined to be one of |↓↓^, |↑↑^, and |T 0 ^, if the first PSB check indicates a blockade, or state |S^ if the first PSB check indicates the absence of a blockade.
  16. 16. The method of claim 15, wherein the two-qubit state is determined to be one of |↓↓^, and |↑↑^, if the second PSB check indicates a blockade, or state |S^ if the second PSB check indicates the absence of a blockade.
  17. 17. The method of claim 16, wherein the two-qubit state is determined to be the target state if the third PSB check indicates a blockade, or state |S^ if the third PSB check indicates the absence of a blockade.
  18. 18. The method of any of claims 1 to 17, wherein the two-qubit state is set at step (i) by pulsing the two spin qubits from a (m+2, n) or (m, n+2) charge state to a (m+1, n+1) charge state, where m and n are arbitrary even numbers.
  19. 19. The method of any of claims 1 to 18, wherein the spin qubits are formed from an electron or hole spin of a silicon quantum dot.
  20. 20. A quantum processing device, comprising: a plurality of spin qubits; and a control arrangement comprising one or more gate electrodes arranged to control the spin state for the plurality of spin qubits, wherein the control arrangement is configured to initialise a pair of spin qubits of the plurality to a target state by: (i) setting the two-qubit state of the pair of spin qubits to any state; (ii) verifying a qubit state associated with the pair of spin qubits against a corresponding target state; and (iii) in response to determining, at step (ii), that the qubit state is not the target state, repeating steps (i) to (ii) until the qubit state is determined as the target state, wherein determining the qubit as the target state involves the control arrangement conducting one or more Pauli-spin blockade (PSB) checks and at least one two-qubit state conversion operation, on the pair of spin qubits.

Description

"Qubit method and device" Cross Reference [0001] The present application claims priority from Australian Provisional Patent Application No 2023902138 filed on 3 July 2023, the contents of which are incorporated herein by reference in their entirety. The contents of the document Huang [1] are incorporated herein by reference in their entirety. Technical Field [0002] This disclosure relates to qubit initialisation in a quantum computing device that is realisable in current quantum technology, such as for example a metal-oxide- semiconductor compatible quantum processor. Background [0003] Quantum computation is an emerging technology developed to outperform current classical transistor-based computation and enable certain tasks in science, engineering, finance, and defence. Having abundant properties and capabilities, quantum bits (qubits) are also more susceptible to noise and difficult to realise compared to classical bits. [0004] Recently, spin qubits in semiconductor have been identified as a relatively suitable implementation with balanced advantages in gate fidelity, interconnectivity, and industrial compatibility. The main challenge drawing most efforts so far is the provision of a low-noise environment, which used to rely on extreme cryogenic cooling to several tens of milli-kelvin and operation at high magnetic fields. [0005] Recent works in strongly confined quantum dots have shown workable qubit control and readout above 1 kelvin at low magnetic field. These relaxed conditions herald a substantial reduction in cryogenic and electronic hardware cost, and moreover enable the integration of a quantum processor in a single cryogenic setup. Qubit initialisation is concerned with preparing a state of one or more qubits, such as spin states, to a target value (i.e., a predetermined desired state). The ability to perform high fidelity qubit initialisation is strongly influenced by the thermal and field conditions. Despite the improvements in qubit control and readout methods, qubit initialisation remains an open challenge. [0006] Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present disclosure. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application. [0007] Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Summary [0008] There is provided a method for qubit initialisation, comprising: (i) setting a two-qubit state of a pair of spin qubits to any state; (ii) verifying a qubit state associated with the pair of spin qubits against a corresponding target state; and (iii) in response to determining, at step (ii), that the qubit state is not the target state, repeating steps (i) to (ii) until the qubit state is determined as the target state, wherein determining the qubit state as the target state includes performing one or more Pauli-spin blockade (PSB) checks and at least one two-qubit state conversion operation on the pair of spin qubits. [0009] In some embodiments, the two-qubit state is reset by performing step (i) in response to one of the one or more PSB checks determining that the two-qubit state is unblockaded. [0010] In some embodiments, each of PSB checks comprises performing a readout operation on the spin qubits of the pair within a PSB lifetime to maintain the two-qubit state in response to the two-qubit state being a blockaded state. [0011] In some embodiments, the qubit state associated with the pair of spin qubits is a single-qubit state of one of the spin qubits of the pair. [0012] In some embodiments, the qubit state associated with the pair of spin qubits is the two-qubit state and the target state is a blockaded state. [0013] In some embodiments, each two-qubit state conversion operation includes a two-qubit gate configured to convert the two-qubit state to an unblockaded state, in response to the two-qubit state being a blockaded state and a different state to the target state. [0014] In some embodiments, each of the PSB checks is a parity PSB check performed over two-qubit basis states of |↓↓^, |↓↑^, |↑↓^, and |↑↑^. [0015] In some embodiments, the target state is an even spin parity state, being one of the |↑↑^ and |↓↓^ states, and wherein the two-qubit gate converts the other of the even states |↑↑^ and |↓↓^ into an odd parity state, being one of the |↑↓^ and |↓↑^ states. [0016] In some embodiments, the target state is |↓↓^ and the two-qubit gate is a zero- control-not gate (zCNOT)