1. Introduction
Let
be a finite dimensional Hilbert space. Given an orthonormal basis
for
, the
(finite) Shannon entropy at a point
is defined as
where
. In 1983, Deutsch derived following uncertainty principle for Shannon entropy [
3].
Theorem 1.1.
(Deutsch Uncertainty Principle) [3] Let , be two orthonormal bases for a finite dimensional Hilbert space . Then
In 1988, followed by a conjecture of Kraus [
9] made in 1987, Maassen and Uffink improved Inequality (
1) [
12].
Theorem 1.2. (Kraus Conjecture/Maassen-Uffink Uncertainty Principle) [9,12] Let , be two orthonormal bases for a finite dimensional Hilbert space . Then
In 2013, Ricaud and Torrésani [
13] showed that Theorem 1.2 holds for Parseval frames.
Theorem 1.3. (Maassen-Uffink-Ricaud-Torrésani Uncertainty Principle) [13] Let , be two Parseval frames for a finite dimensional Hilbert space . Then
Recently, Banach space versions of Deutsch uncertainty principle have been derived in [
11]. To formulate them, we need some notions. Given a Parseval p-frame
for
, we define the
(finite) p-Shannon entropy at a point
as
where
. On the other way, given a Parseval p-frame
for
, we define the
(finite) p-Shannon entropy at a point
as
where
.
Theorem 1.4.
[11] (Functional Deutsch Uncertainty Principle) Let and be Parseval p-frames for a finite dimensional Banach space . Then
Theorem 1.5.
(Functional Deutsch Uncertainty Principle) Let and be two Parseval p-frames for the dual of a finite dimensional Banach space . Then
In this paper, we derive continuous versions of Theorem 1.1, Theorem 1.4 and Theorem 1.5. We also formulate a conjecture based on Theorem 1.2. We wish to say that functional continuous uncertainty principles are derived in [
10].
2. Continuous Deutsch Uncertainty Principle and Continuous Kraus Conjecture
In the paper,
denotes
or
and
(resp.
) denotes a Hilbert space (resp. Banach space) (need not be finite dimensional) over
. We use
to denote a measure space. Continuous frames are introduced independently by Ali, Antoine and Gazeau [
1] and Kaiser [
8]. In the paper,
denotes
or
and
denotes a finite dimensional Hilbert space.
Definition 2.1.
[1,8] Let be a measure space. A collection in a Hilbert space is said to be a continuous Parseval frame for if the following conditions hold.
-
(i)
For each , the map is measurable.
-
(ii)
We consider the following subclass of continuous Parseval frames.
Definition 2.2.
A continuous Parseval frame for is said to be 1-bounded if
Note that if
is a Parseval frame for a Hilbert space
, then
,
(see Remark 3.12 in [
7]). We are unable to derive this for continuous frames. Given a continuous 1-bounded Parseval frame
for
, we define the
continuous Shannon entropy at a point
as
where
. Following is the first fundamental result of this paper.
Theorem 2.3. (Continuous Deutsch Uncertainty Principle) Let , be measure spaces and , be 1-bounded continuous Parseval frames for a Hilbert space . Then
Proof. Since
for all
,
for all
and log is concave, using Jensen’s inequality (cf. [
6]) we get
Let
. Then using Buzano inequality [
2,
5] we get
□
Theorem 2.3 promotes following question.
Question 2.4. Let , be measure spaces, be a Hilbert space. For which pairs of 1-bounded continuous Parseval frames and for , we have equality in Inequality (2)?
Based on Theorems 1.3 and Theorem 2.3 we formulate following conjecture.
Conjecture 2.5. (Continuous Kraus Conjecture) Let , be measure spaces and , be 1-bounded continuous Parseval frames for a Hilbert space . Then
Next we derive continuous Deutsch uncertainty for Banach spaces. We need a definition.
Definition 2.6.
[4] Let be a measure space and be a Banach space over . A collection in is said to be acontinuous Parseval p-frame() for if the following conditions hold.
-
(i)
For each , the map is measurable.
-
(ii)
If , , then we say that the frame is 1-bounded.
Similar to Definition 2.2, we set the following.
Definition 2.7.
A continuous Parseval p-frame for is said to be 1-bounded if
Given a 1-bounded continuous Parseval p-frame
for
, we define the
continuous p-Shannon entropy at a point
as
where
.
Theorem 2.8. (Functional Continuous Deutsch Uncertainty Principle ) Let , be measure spaces and , be 1-bounded continuous Parseval p-frames for a Banach space . Then
Proof. Let
be such that
. Then
which gives
□
Corollary 2.9. Theorem 1.1 follows from Theorem 2.8.
Proof. Let
,
be measure spaces and
,
be 1-bounded continuous Parseval frames for a Hilbert space
. Define
Now by using Buzano inequality [
2,
5] we get
□
Theorem 2.8 brings the following question.
Question 2.10. Let , be measure spaces, be a Banach space and . For which pairs of continuous Parseval p-frames and for , we have equality in Inequality (4)?
Next we derive a dual inequality of (
4). For this we need dual of Definition 2.6.
Definition 2.6. Let be a measure space and be a Banach space over . A collection in is said to be a continuous Parseval p-frame () for if the following conditions hold.
-
(i)
For each , the map is measurable.
-
(ii)
f , , then we say that the frame is 1-bounded.
Given a 1-bounded continuous Parseval p-frame
for
, we define the
continuous p-Shannon entropy at a point
as
where
. We now have the following dual to Theorem 2.8.
Theorem .(Continuous Deutsch Uncertainty Principle for Banach spaces) Let , be measure spaces and , be 1-bounded continuous Parseval p-frames for the dual of a Banach space . Then
Proof. Let
be such that
. Then
which gives
Let
. Then
□
Theorem 2.12 again gives the following question.
Question 2.13. Let , be measure spaces, be a Banach space and . For which pairs of continuous Parseval p-frames and for , we have equality in Inequality (5)
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