Thresholding of qubit phase registers for quantum recommendation systems

1. A system, comprising:

a memory that stores computer executable components; and

a processor, operably coupled to the memory, and that executes the computer executable components stored in the memory, wherein the computer executable components comprise:

a quantum recommendation component that projects a preference vector onto a portion of a Hilbert space based on a value of a qubit phase register, wherein the portion of the Hilbert space encodes singular values of a preference matrix that are greater than or equal to a defined threshold.

2. The system of claim 1 , further comprising:

a binarization component that computes a plurality of binarized phase values based on the defined threshold and the preference matrix.

3. The system of claim 2 , further comprising:

an initialization component that determines a number of threshold qubits comprised within a threshold register based on an amount of significant digits in the plurality of binarized phase values and an amount of qubits comprised within the qubit phase register, wherein the threshold qubits are entangled with quantum states of the qubit phase register to identify the portion of the Hilbert space.

4. The system of claim 2 , further comprising:

an entanglement component that entangles a first threshold qubit from a threshold register to quantum states of the qubit phase register that correspond to a first phase region of the Hilbert space that is less than a first binarized phase value from the plurality of binarized phase values.

5. The system of claim 4 , wherein the entanglement component further entangles a second threshold qubit from the threshold register to quantum states of the qubit phase register that correspond to a second phase region of the Hilbert space that is greater than a second binarized phase value from the plurality of binarized phase values.

6. The system of claim 5 , wherein the entanglement component further entangles a third threshold qubit from the threshold register to the first threshold qubit and the second threshold qubit; and wherein the system further comprises:

a measurement component that determines whether the preference vector is projected onto the portion of the Hilbert space based on a quantum state of the third threshold qubit.

7. The system of claim 6 , wherein the portion of the Hilbert space comprises the first phase region and the second phase region.

8. A computer program product for implementing a thresholding scheme for a qubit phase register, the computer program product comprising a computer readable storage medium having program instructions embodied therewith, the program instructions executable by a processor to cause the processor to:

project, by a system operatively coupled to the processor, a preference vector onto a portion of a Hilbert space based on a value of the qubit phase register, wherein the portion of the Hilbert space encodes singular values of a preference matrix that are greater than or equal to a defined threshold.

9. The computer program product of claim 8 , wherein the program instructions further cause the processor to:

compute, by the system, a plurality of binarized phase values based on the defined threshold and the preference matrix; and

determine, by the system, a number of threshold qubits comprised within a threshold register based on an amount of significant digits in the plurality of binarized phase values and an amount of qubits comprised within the qubit phase register.

10. The computer program product of claim 9 , wherein the program instructions further cause the processor to:

entangle, by the system, a first threshold qubit from the threshold qubits to quantum states of the qubit phase register that correspond to a first phase region of the Hilbert space that is less than a first binarized phase value from the plurality of binarized phase values; and

entangle, by the system, a second threshold qubit from the threshold qubits to quantum states of the qubit phase register that correspond to a second phase region of the Hilbert space that is greater than a second binarized phase value from the plurality of binarized phase values.

11. The computer program product of claim 10 , wherein the program instructions further cause the processor to:

entangle, by the system, a third threshold qubit from the threshold qubits to the first threshold qubit and the second threshold qubit; and

determine, by the system, that the preference vector is projected onto the portion of the Hilbert space based on a quantum state of the third threshold qubit.

12. A system, comprising:

a memory that stores computer executable components; and

a processor, operably coupled to the memory, and that executes the computer executable components stored in the memory, wherein the computer executable components comprise:

a quantum recommendation component that implements a quantum recommendation algorithm using a thresholding scheme that projects a preference vector onto a portion of a Hilbert space based on quantum states of a qubit phase register and a defined threshold.

13. The system of claim 12 , further comprising:

a binarization component that computes a plurality of binarized phase values from the defined threshold, wherein the plurality of binarized phase values define a plurality of phase regions of the Hilbert space upon which to project the preference vector.

14. The system of claim 13 , further comprising:

an entanglement component that entangles a plurality of threshold qubits of a qubit threshold register with the quantum states of the qubit phase register based the plurality of binarized phase values.

15. The system of claim 14 , wherein the entanglement component further entangles another threshold qubit of the qubit threshold register with the plurality of threshold qubits, and wherein the system further comprises:

a measurement component that determines whether the preference vector is projected onto the portion of the Hilbert space based on a quantum state of the another threshold qubit.