What quantum computers may tell us about quantum mechanics

What quantum computers may tell us about quantum mechanicsby Christopher R. Monroe

Presentation by: Maria Jane S. PoncardasMSU-IIT

May 16, 20162:00 PM, CSM-130

What quantum computers may tell us about quantum mechanics

•Quantum Information processing

•Quantum entanglement

•Quantum Computer Hardware

Introduction

• Quantum Mechanics foundations are often questioned due to the difficulty of reconciling it with classical laws of physics.

• Today’s technology leads to the device being miniature towards atomic scale.

• BUT:

• There will be unnecessary QUANTUM TUNNELING of electrons and large signal fluctuations

First transistor created at A&T’s Bell Labs on

December, 1947

First single-electron transistor made entirely

of oxide-based materials, 2011

•These miniaturization arises quantum information processing faster devices in terms of its performance

eclipse the existing technology--- instead of shrinking, we take advantage of the principle

Quantum Mechanics

Information Theory

20th Century

Quantum Information Science21st Century

QUANTUM INFORMATION PROCESSING


• Began from discovery of binary digits or bits by Claude Shannon.

Claude Shannon

• growth in the technology of processing information speed and computing power is described exponentially.

• Chip components also shrink in size as described in Moore’s law.

Recall: Transistor is a device that regulates current or voltage flow and acts as a switch.


• New information arise then as the limit of classical bits are met, such as quantum information processing.

• Quantum bits – simplest mechanical unit of information can store superposition of 0 and 1.

Ψ = α 0 > + β 1 >

where α and β are complex amplitudes of superposition.


• for N qubits, it stores a superposition of 2N binary numbers.

• 2N are possibilities of measurement*

• The trick behind a useful quantum computer is the phenomenon called quantum interference.

--- *complex amplitude interfering to cancel out leaving only few or one answer.*

QUANTUM ENTANGLEMENT

• It is the combination of two properties in QM – superposition and measurement.*

• It is the most misunderstood concept in quantum mechanics.


•Definition 1:

An entangled state is one that is not separable, where measurements are performed on one constituent without affecting the others.

• There is a correlation between subsystems and entangled state*

• High detector quantum efficiency is needed


•Definition 2:

An entangled state is one that is not separable, where highly quantum-efficient measurements are performed on one constituent without affecting the others, and where the constituents are spacelike separated during the measurement time.

• Have considered Bell’s inequality• Requiring space-like separation

QUANTUM COMPUTER HARDWARE

• The definition of quantum entanglement comprise the reference in building a quantum computer.

i.

ii.

Arbitrary unitary operators must be available and controlled to launch an initial state to an arbitrary

entangled state

Measurements of the qubits must be performed with high quantum efficiency.


• Physicists are in search for quantum measurement.

• Theories like Bohmian mechanics, many-worlds interpretations, transactional interpretation and the quantum decoherence theory, does not address the quantum measurement problems.


• There at least one alternative:

“spontaneous wave function collapse”

--the observer collapsed the wave function by simply observing.

• attempts to meld quantum measurement and QM by adding nonlinear stochastic driving field to quantum mechanics that randomly localizes or collapses the wave function

OUTLOOK

This journey towards quantum computers yields at least three possible results:

o a full-blown large-scale quantum computer will be built

o theory of quantum mechanics will be found incomplete

o we can never reach the first possibility due to economic constraints.

References:• https://www.ias.edu/ideas/2014/ambainis-quantum-computing

• http://www.chemistryviews.org/details/news/1054617/Worlds_Smallest_Transistor.html

• Source: http://www.extremetech.com/extreme/175004-the-genesis-of-the-transistor-the-single-greatest-discovery-in-the-last-100-years

• http://history-computer.com/ModernComputer/thinkers/Shannon.html

• https://www.elektormagazine.com/articles/moores-law

• https://www.youtube.com/watch?v=aWLBmapcJRU

• http://www.daviddarling.info/encyclopedia/Q/quantum_entanglement.html

• http://qoqms.phys.strath.ac.uk/research_qc.html

• https://www.engineering.unsw.edu.au/news/quantum-computing-first-two-qubit-logic-gate-in-silicon

• https://en.wikipedia.org/wiki/Bell's_theorem#Original_Bell.27s_inequality

• https://uwaterloo.ca/institute-for-quantum-computing/quantum-computing-101#Superposition-and-entanglement

• https://en.wikipedia.org/wiki/Double-slit_experiment