Layered Architecture for Quantum Computing

Quantum Computing is the new era of technology that uses the principles of Quantum Mechanics (superposition and entanglement) to achieve remarkable speeds that are not possible for a classical computer or a supercomputer. Classical Computer and Super Computers have the same basic unit which is a ‘bit’.

Bit can either be 0 or 1. The bits 0 and 1 represent the states of the transistors connected in the circuit. Quantum computers work on qubits (also called quantum-bits). Now let’s discuss some basic terminologies of revolving around quantum computers:

Qubits: Qubits are the basic units of quantum computers on which all the operations are performed. Qubits can be of the types: trapped ions, superconducting qubits or photonic qubits. For simplicity let’s consider that 1 electron is a qubit. Electron has a spin (either an upward spin or a downward spin).

When an electron is in upward spin it is said to be in state 0 represented as |0> and in a spin-down state it is 1 represented as |1>. Thus, we got two base states that is |0> and |1>.

Superposition: Qubits exists in superposition meaning that at a given time qubits has an equally likely probability to exist in a state of |0> and |1>. Represented as:

???? |0> + ???? |1>; here |????|² + |????|²= 1
???? and ???? represents the probability of qubit being in a state of |0> and |1>.

Entanglement: An important quantum physics concept which occurs when two or more particles becomes correlated in such a way that the state of one particle instantaneously influences the state of the other(s), regardless of the distance between the entangled particles. Entanglement is the name of a magical bond between particles involved in this phenomenon with the message transmission speed more than that of speed of light! (which seems impossible but experiments have proved the phenomena of entanglement)

Now if thinking why do smaller particles like electrons, protons show entanglement and superposition. No answers are available so far. May be when a powerful quantum computer (greater number of qubits with improved error correction rates) would answer these questions.

Quantum Gates: Similar to classical logic gates like OR, AND, XOR. Quantum gates perform logical operations on qubits. Quantum gates are used to construct quantum circuits which are sequences of quantum gates that are applied to a set of qubits. Quantum circuits can be used to perform a wide variety of tasks according to the applied quantum algorithm to achieve the desired results. Few examples quantum gates are: Hadmard gate, Pauli-X, Pauli-Y, Pauli-Z, CNOT gate.

Architecture of Quantum Computers

Quantum Computers are complex machines, thus having a structured architecture makes it easy to separately understand each layer and its functionalities. Below given is the architecture of a quantum processor:

Host Processor Layer: This layer is the top-most layer of the architecture. Comprises of the classical computer and is responsible for interacting with the user.

This layer handles access to networks, large storage arrays which facilitates user interactions, and has a high bandwidth connection to the control processor.

The quantum algorithms are written in classical language before being converted to quantum instruction. This layer runs the algorithm processes, uses inputs given by the user and translates them into instructions for the quantum processor.

Compiles the quantum algorithm into quantum instructions

Stores the instructions in the form of digital information (0’s and 1’s) and then this information is sent to the control processor plane

Also responsible for collecting the results after execution of quantum algorithm.

Control Processor Layer: This layer acts as an interface between the classical host and the quantum processor and the quantum hardware.

Control processor layer is responsible for correct manipulation of physical qubits and gates available in the quantum processor.

It identifies and triggers the proper Hamiltonian or sequence of quantum gate operations and measurement (which are subsequently carried out by the control and measurement plane on the quantum data plane).

These sequences execute the program, provided by the host processor, for implementing a quantum algorithm

The instructions received from the host processor layer are converted into low level control signal or analog signals that can be understood by the quantum hardware that is the control and measurement layer.

Control and Measurement Layer: This layer controls the physical qubits. Resides on top of the quantum plane.

The analog signals received from the control processor layer are used to generate microwave signals or IR signals of the required frequency. Each physical qubit is attached to the control and measurement layer via wires.

The desired qubit is sent signals during the execution of the quantum algorithms

This layer is responsible for performing quantum operations and measurement on the qubits by applying microwave pulses to the qubits and detecting their response.

Different electronic components, such as microwave generators, amplifiers and detectors are present in this layer

Detectors are used to read the output of the state changed after the quantum operation performed on the qubit

The measurement outcomes are sent back to the classical processor for further processing

Quantum Layers: The quantum layer is the most challenging layers of the quantum computer to build, as it is responsible for creating and maintain the quantum states of the qubits

It consists of qubits and quantum gates.

Qubits can be implemented in a variety of different ways, such as using superconducting circuits, trapped ions, or photons.

After sending the signals to the qubits the change in its state is read by the control and measurement layer and the sent to the host processor as the output after performing the computations.

Qubits at the quantum layer are suspectable to environmental noise and heat. Therefore, environment around the quantum computer need to be controlled very efficiently other the quantum bits will lose the results thus the information is lost. This temperature is controlled in the following approaches:

Room Temperature Control: Refers to the temperature in the range of 20-25 degrees Celsius

(68-77 degree Fahrenheit). This temperature is for general environment comfort of electronic devices, computer. This temperature ensures optimal working of the electronic devices supporting the quantum processor. Doesn’t directly involve in the cooling of the quantum processor.

Cryogenic Control: A cooling system that maintains temperature close to absolute zero, which is 0 Kelvin (-273.15 degrees Celsius or -459.67 degrees Fahrenheit). Cryogenic temperature reduces thermal noise and maintains quantum coherence in the qubits, enabling stable quantum operations.

Cryogenic control systems are crucial components of quantum computers, ensuring the integrity of quantum information processing.