Unit of information and future of Computing
Software Engineering Department
San Jose State University
San Jose, USA email@example.com Abstract— Qubit is a unit of quantum information in quantum computing. A classical computer performs operation using classical bits, which can be either 0 or 1. In contrast a quantum computer uses quantum bits or qubits and they can be both 0 and
1 at the same time. And it is this feature that gives quantum computer its superior computing power. There are number of physical objects that can be used as qubits for example metal rings embedded in a solid state substrate, coherent state of light, quantum dots, an atom etc. This report focuses on using outer most electron of phosphorus atom as qubit.
Quantum object used for qubits behaves in laws with quantum mechanics. Qubits make quantum computer more superior than classical computer because it uses special and strange properties of quantum world. Properties used by qubits are superposition, entanglement, quantum tunneling etc.
Superposition is a quantum phenomena in which object is in more than one state at once. But when observed, it gives a result corresponding to only one possible state.
Index Terms—Quantum Computing, Quantum computers,
Quantum Bits, Qubits, quantum spin
Quantum computers are completely new and entirely different kind of the computers. Quantum mechanics is the branch of physics that observes the behavior of fundamental elementary particles at nanoscopic scales that make up the universe. Quantum mechanics provides mathematical description of dual particle like and wave like behavior and interaction of energy and matter.
A conventional computer works through transistors. A transistor can be in two different states ON and OFF also known as ones and zeros. These states are known as binary digits or bits. Quantum computer works by taking the properties of quantum mechanics and applying them to computers. Instead of using transistors to compute the data, quantum computers uses quantum objects as a special kind of transistor known as quantum binary digits or qubits.
Fig 1.1 Electron spin denotes 1 and 0 similar to binary bits
Fig 1.2 Quantum superposition – Electron is in both 1 and 0 state at same time.
One regular bit provides two possible states 0 and 1, with two regular bits provide four possible states 00, 01, 10 and 11.
The compute can only output one of those variants. But when we have two qubits contains four bits of information due to superposition. So the amount of equivalent classical information contains by n qubits is 2n (2 to the power of n).
Therefore the number of operations performed by quantum computer using qubits to arrive at the result is exponentially smaller than classical bit.
Fig 2.2 Electron moves in external magnetic pulse
Fig 1.3 Two Qubits can store up to 4 bits of information
Researchers have created qubit using many techniques. This paper describes how to use outermost electron of phosphorus atom as qubit. Phosphorus atom is embedded in silicon crystal, right next to a tiny transistor. Electron has it electronic dipole called its spin. It had two orientations up é or down ê . When electron is in spin up state it is considered as |1> while spin down state is considered as |0> like classical bit.
Fig 2.1 Phosphorus atom in Transistor
A strong magnetic field is applied to differentiate the electron from spin up to spin down or vice versa. This strong magnetic field is achieved by using super-conducting magnets.
A super-conducting magnet is a large solenoid, a coil of super conducting wire, packed in cylindrical vessel filled full of liquid helium. Electrons are not in a stable state to perform any operation on it and will be bouncing around at room temperature. So in order to work with electron in a stable state environmental condition are changed. The apparatus or naïve quantum computer is cooled to absolute zero. At absolute zero there will