In the previous blog, I had discussed quantum mechanics, its basic fundamentals and how it is different from classical computing. So before going through this blog, if you are not aware about the fundamentals of quantum computing and quantum mechanics, you can check out my previous blog.
In this blog, I will discuss what Quantum Qubit is and how it differs from classical logical bit and how qubit is created.
Classical Bit:
A bit is a binary unit of information used in classical computation. It stores only two values 0 or 1. Either there is a current flow i.e. 1 or no current flow i.e., 0. There is 2^n possible states, only one at a time. Everything i.e. our computers, supercomputers, servers, calculators etc stores the information using classical bit.
Creating a Classical Bit:
In modern day computers, transistors act as switches. Using the electricity flow to denote which information is saved. If flowing electrons or voltage is applied to base of circuit then 1, if voltage is removed then 0.
Transistors combine to form logic gates.
Logic gates are grouped into modules which can perform bitwise operation. Combinations to these gates form a circuit chip.
Classical Bit processing:
Every data can be represented as binary.
For e.g.: The word ‘bat’ in ASCII is ’98 97 116' and converted to binary as ‘1100010 1100001 1110100’.
Like this, all types of files can be represented as binary. The processor does calculations and gives processed output. Not only text files, but also image files, audio files all are converted to binary and stored on the computers.
For example, for storing audio files, audio at first is converted into digital format using Analog to Digital Converter and after that it is passed on to Digital signal processor which processes the converted digital format by manipulating them and stores it into the memory using bits.
And when reading the stored audio in digital format in memory, Digital Signal Processor will read the digital format and then after processing, the processed digital data will pass through Digital to Analog Converter and then we get audio from the speakers connected to the computer systems.
This is how computer systems store bits and process the information using the bits.
Quantum Qubit:
The bit in quantum world is called Qubit. A qubit or quantum bit is the basic unit of quantum information.
Qubits can be in a 1 or 0 states just like as classical bit, but there is a catch here
there can be a 0 and 1 state at the same time.
This property called superposition of quantum particles is used in quantum computing.
There is 2^n possible states. It can be in all states at the same time. Here Qubits will also have the equivalent number of bits as that of classical bits one at a time, but the advantage here is that it can use all the bits at same time.
For example: if we have 3 qubits then there will be 8 equivalent classical bits, which means at the same time quantum computer can use all the 8 bits.
How Qubit is faster than Bit:
A classical bit can only do one single calculation at a given period of time, whereas Qubit can exist simultaneously in multiple states. This is the great advantage when doing parallel processing tasks.
Qubit can be used for multiple database search or in Artificial Intelligence and Machine learning for training deep learning models to learn the model parameters by parallelising the tasks so that very complex and large models can be trained fast.
How Qubit is created:
Qubits are made using physical systems, such as the spin of an electron or the orientation of photon.
For classical bit, we are considering only flow of electrons to determining the bit whether it is ‘0’ or ‘1’ but for qubit we are considering a spin of electron or orientation of photon to determine a state of qubit.
From the figure above we can either spin the electron up and consider it is in ‘1’ state or spin the electron down and consider it is in ‘0’ state.
But the problem is, in normal room temperature we cannot control the motion of electrons to determine the states, because electrons will be in vibrating state as it is gaining energy from our surroundings.
To control the motion of electrons, we need to cool it down to nearly absolute zero temperature to keep the electrons in a less vibrating low energy state.
We can precisely control the spin or polarity of the quantum particles using particles.
As shown above the image of apparatus, as we go down it is cooling down the temperature and at the very bottom, we will be having quantum processor to generate or control qubits. It will be having peculiar kind of shape like an inverted cake.
As we go down, the temperature will be decreasing and it will reach absolute zero at the bottom and at absolute zero temperature, electrons will be having less energy and in less vibrating state.
And at that state, we can use precision microwaves to spin or flip the electrons to harness the concept of quantum computing.
Quantum Qubit State Representation:
Qubit need two more variables to denote its value based on its position in the “Bloch sphere”
For classical bit, if the switch is on it will be ‘1’ or if the switch is off then it will be ‘0’.
For representing the Qubit, we are not using the switch’s ON/OFF state, we are using the spin position of electron to give state of the Qubit.
At first, the electron will be in a very low energy state i.e in ‘0’ state, and when we are applying a small amount of microwave then the electron will be having a small spin. As we apply more and more amount of microwave then we can spin the electron to ‘1’ state or high energy position.
And in between low energy position to high energy position we are having literally tons of points as it can be seen in above image of “Bloch Sphere”
And to denote the exact position of electron in “Bloch Sphere” we need some kind of notation known as “Dirac” notation.
A Dirac (introduced by Paul Dirac) Bra-Ket notation <|> used to describe the value of a qubit as a vector in sphere.
So, if we want to know the position of our particle, then we can say 60 percent probability of getting 1 and 40 percent of probability getting to 0. We can say that our particle is in superposition state, and when we visualize our particle then we can say that there is 60 percent of chance that our particle will be in ‘1’ state.
This is how Qubit is created and its states are represented.
I hope you enjoyed this blog and learned about how classical bit differs from Quantum bit and how they are created. If you liked this blog, do clap the blog. Don't forget to share this blog amongst your peers.
In my next blog in this quantum computing series, I will discuss how Qubits are retained, stored and how to read qubits.
Thank you for reading.